diff --git a/admin/tool/dataprivacy/tests/expired_contexts_test.php b/admin/tool/dataprivacy/tests/expired_contexts_test.php
index 4b8680c4d7a7..d851000ba6a0 100644
--- a/admin/tool/dataprivacy/tests/expired_contexts_test.php
+++ b/admin/tool/dataprivacy/tests/expired_contexts_test.php
@@ -867,7 +867,7 @@ public function test_process_user_context_with_override_unexpired_role(): void {
     /**
      * Ensure that a module context previously flagged as approved is removed with appropriate unexpiredroles kept.
      */
-    public function test_process_course_context_with_override_unexpired_role() {
+    public function test_process_course_context_with_override_unexpired_role(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -955,7 +955,7 @@ public function test_process_course_context_with_override_unexpired_role() {
     /**
      * Ensure that a module context previously flagged as approved is removed with appropriate expiredroles kept.
      */
-    public function test_process_course_context_with_override_expired_role() {
+    public function test_process_course_context_with_override_expired_role(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -1043,7 +1043,7 @@ public function test_process_course_context_with_override_expired_role() {
     /**
      * Ensure that a module context previously flagged as approved is removed with appropriate expiredroles kept.
      */
-    public function test_process_course_context_with_user_in_both_lists() {
+    public function test_process_course_context_with_user_in_both_lists(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -1132,7 +1132,7 @@ public function test_process_course_context_with_user_in_both_lists() {
     /**
      * Ensure that a module context previously flagged as approved is removed with appropriate expiredroles kept.
      */
-    public function test_process_course_context_with_user_in_both_lists_expired() {
+    public function test_process_course_context_with_user_in_both_lists_expired(): void {
         global $DB;
         $this->resetAfterTest();
 
diff --git a/admin/tool/dataprivacy/tests/manager_observer_test.php b/admin/tool/dataprivacy/tests/manager_observer_test.php
index 7296eb181d1e..4902dcd2c849 100644
--- a/admin/tool/dataprivacy/tests/manager_observer_test.php
+++ b/admin/tool/dataprivacy/tests/manager_observer_test.php
@@ -32,7 +32,7 @@ class manager_observer_test extends data_privacy_testcase {
     /**
      * Ensure that when users are configured as DPO, they are sent an message upon failure.
      */
-    public function test_handle_component_failure() {
+    public function test_handle_component_failure(): void {
         $this->resetAfterTest();
 
         // Create another user who is not a DPO.
diff --git a/admin/tool/generator/tests/maketestcourse_test.php b/admin/tool/generator/tests/maketestcourse_test.php
index a257a42262c1..11670ec10f19 100644
--- a/admin/tool/generator/tests/maketestcourse_test.php
+++ b/admin/tool/generator/tests/maketestcourse_test.php
@@ -30,7 +30,7 @@ class maketestcourse_test extends \advanced_testcase {
     /**
      * Creates a small test course and checks all the components have been put in place.
      */
-    public function test_make_xs_course() {
+    public function test_make_xs_course(): void {
         global $DB;
 
         $this->resetAfterTest();
diff --git a/admin/tool/policy/tests/api_test.php b/admin/tool/policy/tests/api_test.php
index 7a7605a23e6c..ee4973f2b3b5 100644
--- a/admin/tool/policy/tests/api_test.php
+++ b/admin/tool/policy/tests/api_test.php
@@ -193,7 +193,7 @@ public function test_policy_sortorder(): void {
     /**
      * Test that list of policies can be filtered by audience
      */
-    public function test_list_policies_audience() {
+    public function test_list_policies_audience(): void {
         $this->resetAfterTest();
         $this->setAdminUser();
 
diff --git a/cache/tests/administration_helper_test.php b/cache/tests/administration_helper_test.php
index b61cc087a8a0..49b3dd1a06fd 100644
--- a/cache/tests/administration_helper_test.php
+++ b/cache/tests/administration_helper_test.php
@@ -60,7 +60,7 @@ public static function tearDownAfterClass(): void {
     /**
      * Test the numerous summaries the helper can produce.
      */
-    public function test_get_summaries() {
+    public function test_get_summaries(): void {
         // First the preparation.
         $config = cache_config_writer::instance();
         $this->assertTrue($config->add_store_instance('summariesstore', 'file'));
diff --git a/calendar/tests/event_factory_test.php b/calendar/tests/event_factory_test.php
index 3fabf8e85592..b571aa7ea90f 100644
--- a/calendar/tests/event_factory_test.php
+++ b/calendar/tests/event_factory_test.php
@@ -85,7 +85,7 @@ public function test_create_instance(
     /**
      * Test invalid callback exception.
      */
-    public function test_invalid_action_callback() {
+    public function test_invalid_action_callback(): void {
         $this->resetAfterTest(true);
         $this->setAdminUser();
         $event = $this->create_event();
@@ -135,7 +135,7 @@ function () {
     /**
      * Test invalid callback exception.
      */
-    public function test_invalid_visibility_callback() {
+    public function test_invalid_visibility_callback(): void {
         $this->resetAfterTest(true);
         $this->setAdminUser();
         $event = $this->create_event();
@@ -185,7 +185,7 @@ function () {
     /**
      * Test invalid callback exception.
      */
-    public function test_invalid_bail_callback() {
+    public function test_invalid_bail_callback(): void {
         $this->resetAfterTest(true);
         $this->setAdminUser();
         $event = $this->create_event();
@@ -235,7 +235,7 @@ function () {
     /**
      * Test the factory's course cache.
      */
-    public function test_course_cache() {
+    public function test_course_cache(): void {
         $this->resetAfterTest(true);
         $this->setAdminUser();
         $course = self::getDataGenerator()->create_course();
@@ -288,7 +288,7 @@ function () {
     /**
      * Test the factory's module cache.
      */
-    public function test_module_cache() {
+    public function test_module_cache(): void {
         $this->resetAfterTest(true);
         $this->setAdminUser();
         $course = self::getDataGenerator()->create_course();
diff --git a/calendar/tests/event_vault_test.php b/calendar/tests/event_vault_test.php
index d03ab45ea80b..c8c29368325b 100644
--- a/calendar/tests/event_vault_test.php
+++ b/calendar/tests/event_vault_test.php
@@ -196,7 +196,7 @@ public function test_get_action_events_by_timesort_between_time_after_event(): v
      * provided timesort values and the last seen event can be provided to
      * get paginated results.
      */
-    public function test_get_action_events_by_timesort_between_time_skip_even_records() {
+    public function test_get_action_events_by_timesort_between_time_skip_even_records(): void {
         $this->resetAfterTest(true);
         $this->setAdminuser();
 
@@ -247,7 +247,7 @@ public function test_get_action_events_by_timesort_between_time_skip_even_record
      * number of events requested has been satisfied. In this case the first
      * five events are rejected so it should require two database requests.
      */
-    public function test_get_action_events_by_timesort_between_time_skip_first_records() {
+    public function test_get_action_events_by_timesort_between_time_skip_first_records(): void {
         $this->resetAfterTest(true);
         $this->setAdminuser();
 
@@ -423,7 +423,7 @@ public function test_get_action_events_by_timesort_non_consecutive_ids(): void {
      * - A user in group B should see only the B override
      * - A user in both A and B should see both
      */
-    public function test_get_action_events_by_timesort_with_identical_group_override_priorities() {
+    public function test_get_action_events_by_timesort_with_identical_group_override_priorities(): void {
         $this->resetAfterTest();
         $this->setAdminuser();
 
@@ -804,7 +804,7 @@ public function test_get_action_events_by_course_between_time_after_event(): voi
      * provided timesort values and the last seen event can be provided to
      * get paginated results.
      */
-    public function test_get_action_events_by_course_between_time_skip_even_records() {
+    public function test_get_action_events_by_course_between_time_skip_even_records(): void {
         $user = $this->getDataGenerator()->create_user();
         $course1 = $this->getDataGenerator()->create_course();
         $course2 = $this->getDataGenerator()->create_course();
@@ -870,7 +870,7 @@ public function test_get_action_events_by_course_between_time_skip_even_records(
      * number of events requested has been satisfied. In this case the first
      * five events are rejected so it should require two database requests.
      */
-    public function test_get_action_events_by_course_between_time_skip_first_records() {
+    public function test_get_action_events_by_course_between_time_skip_first_records(): void {
         $user = $this->getDataGenerator()->create_user();
         $course1 = $this->getDataGenerator()->create_course();
         $course2 = $this->getDataGenerator()->create_course();
@@ -1080,7 +1080,7 @@ public function test_get_action_events_by_course_non_consecutive_ids(): void {
      * - A user in group B should see only the B override
      * - A user in both A and B should see both
      */
-    public function test_get_action_events_by_course_with_identical_group_override_priorities() {
+    public function test_get_action_events_by_course_with_identical_group_override_priorities(): void {
         $this->resetAfterTest();
         $this->setAdminuser();
 
diff --git a/calendar/tests/externallib_test.php b/calendar/tests/externallib_test.php
index 33ee8a22d90b..e987aaa7eac0 100644
--- a/calendar/tests/externallib_test.php
+++ b/calendar/tests/externallib_test.php
@@ -1425,7 +1425,7 @@ public function test_get_calendar_action_events_by_course_with_search(): void {
      * Test that get_action_events_by_courses will return a list of events for each
      * course you provided as long as the user is enrolled in the course.
      */
-    public function test_get_action_events_by_courses() {
+    public function test_get_action_events_by_courses(): void {
         $user = $this->getDataGenerator()->create_user();
         $course1 = $this->getDataGenerator()->create_course();
         $course2 = $this->getDataGenerator()->create_course();
@@ -1558,7 +1558,7 @@ public function test_get_action_events_by_courses() {
     /**
      * Test get_action_events_by_courses with search feature
      */
-    public function test_get_action_events_by_courses_with_search() {
+    public function test_get_action_events_by_courses_with_search(): void {
         // Generate data.
         $user = $this->getDataGenerator()->create_user();
         $course1 = $this->getDataGenerator()->create_course();
diff --git a/calendar/tests/std_proxy_test.php b/calendar/tests/std_proxy_test.php
index 9658a6098faa..af3080df9790 100644
--- a/calendar/tests/std_proxy_test.php
+++ b/calendar/tests/std_proxy_test.php
@@ -54,7 +54,7 @@ public function setUp(): void {
      * @param string $member   Object member to retrieve.
      * @param mixed  $expected Expected value of member.
      */
-    public function test_proxy($id, $member, $expected) {
+    public function test_proxy($id, $member, $expected): void {
         $proxy = new std_proxy($id, function($id) {
             return $this->objects[$id];
         });
@@ -70,7 +70,7 @@ public function test_proxy($id, $member, $expected) {
      * @param string $member      Object member to retrieve.
      * @param mixed  $storedvalue Value as would be stored externally.
      */
-    public function test_base_values($id, $member, $storedvalue) {
+    public function test_base_values($id, $member, $storedvalue): void {
         $proxy = new std_proxy(
             $id,
             function($id) {
@@ -89,7 +89,7 @@ function($id) {
      * @dataProvider get_set_testcases
      * @param int $id ID of the object being proxied.
      */
-    public function test_get_invalid_member($id) {
+    public function test_get_invalid_member($id): void {
         $proxy = new std_proxy($id, function($id) {
             return $this->objects[$id];
         });
@@ -104,7 +104,7 @@ public function test_get_invalid_member($id) {
      * @dataProvider get_set_testcases
      * @param int $id Object ID.
      */
-    public function test_get_proxied_instance($id) {
+    public function test_get_proxied_instance($id): void {
         $proxy = new std_proxy($id, function($id) {
             return $this->objects[$id];
         });
diff --git a/competency/tests/privacy/provider_test.php b/competency/tests/privacy/provider_test.php
index 2e8f39aa8ea8..dff9fe5cf1da 100644
--- a/competency/tests/privacy/provider_test.php
+++ b/competency/tests/privacy/provider_test.php
@@ -1999,7 +1999,7 @@ public function test_export_data_for_user_with_related_learning_plans(): void {
         $this->assert_exported_comments(['Hi.'], $data->comments);
     }
 
-    public function test_export_data_for_user_with_related_competencies() {
+    public function test_export_data_for_user_with_related_competencies(): void {
         $path = [
             get_string('competencies', 'core_competency'),
             get_string('privacy:path:relatedtome', 'core_competency'),
diff --git a/course/tests/backup/restore_test.php b/course/tests/backup/restore_test.php
index 26ebb90dc317..bfd98f5752bc 100644
--- a/course/tests/backup/restore_test.php
+++ b/course/tests/backup/restore_test.php
@@ -387,7 +387,7 @@ public function test_restore_course_info_in_new_course(): void {
         $this->assertEquals($startdate, $c2->startdate);
     }
 
-    public function test_restore_course_with_users() {
+    public function test_restore_course_with_users(): void {
         global $DB;
         $this->resetAfterTest();
         $this->setAdminUser();
diff --git a/course/tests/caching_content_item_readonly_repository_test.php b/course/tests/caching_content_item_readonly_repository_test.php
index ffb76c639018..9ea96b426f41 100644
--- a/course/tests/caching_content_item_readonly_repository_test.php
+++ b/course/tests/caching_content_item_readonly_repository_test.php
@@ -39,7 +39,7 @@ class caching_content_item_readonly_repository_test extends \advanced_testcase {
     /**
      * Test verifying that content items are cached and returned from the cache in subsequent same-request calls.
      */
-    public function test_find_all_for_course() {
+    public function test_find_all_for_course(): void {
         $this->resetAfterTest();
         global $DB;
 
diff --git a/course/tests/category_test.php b/course/tests/category_test.php
index c1ec14a69975..f17709fce11f 100644
--- a/course/tests/category_test.php
+++ b/course/tests/category_test.php
@@ -751,7 +751,7 @@ public function test_course_contacts(): void {
         $CFG->coursecontact = $oldcoursecontact;
     }
 
-    public function test_course_contacts_with_duplicates() {
+    public function test_course_contacts_with_duplicates(): void {
         global $DB, $CFG;
 
         set_config('coursecontactduplicates', true);
diff --git a/course/tests/content_item_readonly_repository_test.php b/course/tests/content_item_readonly_repository_test.php
index 84406076c093..8a6b30aff565 100644
--- a/course/tests/content_item_readonly_repository_test.php
+++ b/course/tests/content_item_readonly_repository_test.php
@@ -76,7 +76,7 @@ public function test_find_all_for_course_hidden_module(): void {
     /**
      * Test confirming that all content items can be fetched, even those which require certain caps when in a course.
      */
-    public function test_find_all() {
+    public function test_find_all(): void {
         $this->resetAfterTest();
 
         global $DB, $CFG;
diff --git a/course/tests/courselib_test.php b/course/tests/courselib_test.php
index 7fdaf62202fb..45338180d388 100644
--- a/course/tests/courselib_test.php
+++ b/course/tests/courselib_test.php
@@ -4582,7 +4582,7 @@ public function get_course_classify_courses_for_timeline_test_cases() {
      * @param array $coursesdata Courses to create
      * @param array $expected Expected test results.
      */
-    public function test_course_classify_courses_for_timeline($coursesdata, $expected) {
+    public function test_course_classify_courses_for_timeline($coursesdata, $expected): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
 
@@ -4723,7 +4723,7 @@ public function test_course_get_enrolled_courses_for_logged_in_user(
         $offset,
         $expecteddbqueries,
         $expectedresult
-    ) {
+    ): void {
         global $DB;
 
         $this->resetAfterTest();
@@ -4908,7 +4908,7 @@ public function get_course_filter_courses_by_timeline_classification_test_cases(
     /**
      * Test the course_get_enrolled_courses_for_logged_in_user_from_search function.
      */
-    public function test_course_get_enrolled_courses_for_logged_in_user_from_search() {
+    public function test_course_get_enrolled_courses_for_logged_in_user_from_search(): void {
         global $DB;
 
         // Set up.
@@ -5021,7 +5021,7 @@ public function test_course_filter_courses_by_timeline_classification(
         $offset,
         $expectedcourses,
         $expectedprocessedcount
-    ) {
+    ): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
 
@@ -5242,7 +5242,7 @@ public function test_course_filter_courses_by_customfield(
         $offset,
         $expectedcourses,
         $expectedprocessedcount
-    ) {
+    ): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
 
@@ -5487,7 +5487,7 @@ public function test_course_filter_courses_by_timeline_classification_with_hidde
         $expectedcourses,
         $expectedprocessedcount,
         $hiddencourse
-    ) {
+    ): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
         $student = $generator->create_user();
@@ -6983,7 +6983,7 @@ public function test_course_get_course_dates_for_user_ids(
         $enrolmentmethods,
         $enrolled,
         $expected
-    ) {
+    ): void {
         global $DB;
         $this->resetAfterTest();
 
diff --git a/course/tests/externallib_test.php b/course/tests/externallib_test.php
index a560bf98674b..606af80929c3 100644
--- a/course/tests/externallib_test.php
+++ b/course/tests/externallib_test.php
@@ -3747,7 +3747,7 @@ public function test_get_enrolled_courses_by_timeline_classification(
         $expectednextoffset,
         $expectedexception = null,
         $searchvalue = null
-    ) {
+    ): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
 
@@ -3979,7 +3979,7 @@ public function test_get_enrolled_users_by_cmid(): void {
     /**
      * Verify that content items can be added to user favourites.
      */
-    public function test_add_content_item_to_user_favourites() {
+    public function test_add_content_item_to_user_favourites(): void {
         $this->resetAfterTest();
 
         $course = $this->getDataGenerator()->create_course();
@@ -4017,7 +4017,7 @@ public function test_add_content_item_to_user_favourites() {
     /**
      * Verify that content items can be removed from user favourites.
      */
-    public function test_remove_content_item_from_user_favourites() {
+    public function test_remove_content_item_from_user_favourites(): void {
         $this->resetAfterTest();
 
         $course = $this->getDataGenerator()->create_course();
@@ -4057,7 +4057,7 @@ public function test_remove_content_item_from_user_favourites() {
     /**
      * Test the web service returning course content items for inclusion in activity choosers, etc.
      */
-    public function test_get_course_content_items() {
+    public function test_get_course_content_items(): void {
         $this->resetAfterTest();
 
         $course  = self::getDataGenerator()->create_course();
diff --git a/enrol/lti/tests/local/ltiadvantage/repository/published_resource_repository_test.php b/enrol/lti/tests/local/ltiadvantage/repository/published_resource_repository_test.php
index 58bc5635d685..9a9baac241b4 100644
--- a/enrol/lti/tests/local/ltiadvantage/repository/published_resource_repository_test.php
+++ b/enrol/lti/tests/local/ltiadvantage/repository/published_resource_repository_test.php
@@ -98,7 +98,7 @@ protected function generate_published_resources() {
      *
      * @covers ::find_all_for_user
      */
-    public function test_find_all_for_user() {
+    public function test_find_all_for_user(): void {
         $this->resetAfterTest();
         [$user, $user2, $user3, $course, $course2, $mod, $mod2, $mod3, $mod4] = $this->generate_published_resources();
 
@@ -131,7 +131,7 @@ public function test_find_all_for_user() {
      *
      * @covers ::find_all_by_ids_for_user
      */
-    public function test_find_all_by_ids_for_user() {
+    public function test_find_all_by_ids_for_user(): void {
         $this->resetAfterTest();
         [$user, $user2, $user3, $course, $course2, $mod, $mod2, $mod3, $mod4, $coursetool, $tool, $tool2, $tool3, $tool4] =
             $this->generate_published_resources();
diff --git a/enrol/lti/tests/local/ltiadvantage/repository/resource_link_repository_test.php b/enrol/lti/tests/local/ltiadvantage/repository/resource_link_repository_test.php
index 4526cb3ab3ff..7d69fdb41210 100644
--- a/enrol/lti/tests/local/ltiadvantage/repository/resource_link_repository_test.php
+++ b/enrol/lti/tests/local/ltiadvantage/repository/resource_link_repository_test.php
@@ -167,7 +167,7 @@ public function test_find(): void {
      *
      * @covers ::find_by_resource
      */
-    public function test_find_by_resource() {
+    public function test_find_by_resource(): void {
         $this->resetAfterTest();
         $resourcelink = $this->generate_resource_link();
         $repository = new resource_link_repository();
@@ -196,7 +196,7 @@ public function test_find_by_resource() {
      *
      * @covers ::find_by_resource_and_user
      */
-    public function test_find_by_resource_and_user() {
+    public function test_find_by_resource_and_user(): void {
         global $CFG;
         $this->resetAfterTest();
         $resourcelink = $this->generate_resource_link();
diff --git a/enrol/lti/tests/local/ltiadvantage/task/sync_members_test.php b/enrol/lti/tests/local/ltiadvantage/task/sync_members_test.php
index 3db54e83d4a4..eccca4c60091 100644
--- a/enrol/lti/tests/local/ltiadvantage/task/sync_members_test.php
+++ b/enrol/lti/tests/local/ltiadvantage/task/sync_members_test.php
@@ -726,7 +726,7 @@ public function test_sync_non_lti_linked_user(): void {
      * @covers ::execute
      */
     public function test_sync_enrolments_and_migration(?array $legacydata, ?array $resourceconfig, array $launchdata,
-            ?array $syncmembers, array $expected) {
+            ?array $syncmembers, array $expected): void {
 
         $this->resetAfterTest();
 
diff --git a/enrol/lti/tests/local/ltiadvantage/task/sync_tool_grades_test.php b/enrol/lti/tests/local/ltiadvantage/task/sync_tool_grades_test.php
index f661e03ab080..72b95b813ba0 100644
--- a/enrol/lti/tests/local/ltiadvantage/task/sync_tool_grades_test.php
+++ b/enrol/lti/tests/local/ltiadvantage/task/sync_tool_grades_test.php
@@ -743,7 +743,7 @@ public function test_sync_grades_failed_service_call(): void {
      *
      * @covers ::execute
      */
-    public function test_sync_grades_coupled_lineitem() {
+    public function test_sync_grades_coupled_lineitem(): void {
         $this->resetAfterTest();
 
         [$course, $resource] = $this->create_test_environment();
@@ -817,7 +817,7 @@ public function test_sync_grades_coupled_lineitem() {
      *
      * @covers ::execute
      */
-    public function test_sync_grades_none_or_many_lineitems_activity_context() {
+    public function test_sync_grades_none_or_many_lineitems_activity_context(): void {
         $this->resetAfterTest();
 
         [$course, $resource] = $this->create_test_environment();
@@ -894,7 +894,7 @@ public function test_sync_grades_none_or_many_lineitems_activity_context() {
      *
      * @covers ::execute
      */
-    public function test_sync_grades_none_or_many_lineitems_course_context() {
+    public function test_sync_grades_none_or_many_lineitems_course_context(): void {
         $this->resetAfterTest();
 
         [$course, $tool1, $tool2, $resource] = $this->create_test_environment();
diff --git a/enrol/tests/enrollib_test.php b/enrol/tests/enrollib_test.php
index 2280c144741b..b19530f67262 100644
--- a/enrol/tests/enrollib_test.php
+++ b/enrol/tests/enrollib_test.php
@@ -1308,7 +1308,7 @@ public function test_enrol_get_my_courses_sort_by_last_access(
         $limit,
         $offset,
         $expectedcourses
-    ) {
+    ): void {
         global $DB, $CFG;
 
         $this->resetAfterTest();
diff --git a/lib/dml/tests/dml_test.php b/lib/dml/tests/dml_test.php
index b00b1f897dba..f93189cc40cd 100644
--- a/lib/dml/tests/dml_test.php
+++ b/lib/dml/tests/dml_test.php
@@ -533,7 +533,7 @@ public function test_add_sql_debugging(): void {
      *
      * @covers ::add_sql_debugging
      */
-    public function test_sql_debugging_anon_class() {
+    public function test_sql_debugging_anon_class(): void {
         global $CFG;
         $CFG->debugsqltrace = 100;
 
diff --git a/lib/filebrowser/tests/file_browser_test.php b/lib/filebrowser/tests/file_browser_test.php
index 6d0123bbd077..5044a810b46f 100644
--- a/lib/filebrowser/tests/file_browser_test.php
+++ b/lib/filebrowser/tests/file_browser_test.php
@@ -109,7 +109,7 @@ public function setUp(): void {
     /**
      * Test "Server files" from the system context
      */
-    public function test_file_info_context_system() {
+    public function test_file_info_context_system(): void {
 
         // There is one non-empty category child and two category children.
 
@@ -126,7 +126,7 @@ public function test_file_info_context_system() {
     /**
      * Test "Server files" from the system context, hide Misc category
      */
-    public function test_file_info_context_system_hidden() {
+    public function test_file_info_context_system_hidden(): void {
 
         // Hide the course category that contains our two courses. Teacher does not have cap to view hidden categories.
         \core_course_category::get($this->course1->category)->update(['visible' => 0]);
@@ -153,7 +153,7 @@ public function test_file_info_context_system_hidden() {
     /**
      * Test "Server files" from the course category context
      */
-    public function test_file_info_context_coursecat() {
+    public function test_file_info_context_coursecat(): void {
 
         // There are two non-empty courses.
 
@@ -183,7 +183,7 @@ public function test_file_info_context_coursecat_jpg(): void {
     /**
      * Test "Server files" from the course context (course1)
      */
-    public function test_file_info_context_course_1() {
+    public function test_file_info_context_course_1(): void {
 
         $browser = get_file_browser();
         $fileinfo = $browser->get_file_info(\context_course::instance($this->course1->id));
@@ -214,7 +214,7 @@ public function test_file_info_context_course_1() {
     /**
      * Test "Server files" from the course context (course1)
      */
-    public function test_file_info_context_course_2() {
+    public function test_file_info_context_course_2(): void {
 
         // 2. Start from the course level.
         $browser = get_file_browser();
diff --git a/lib/filestorage/tests/file_storage_test.php b/lib/filestorage/tests/file_storage_test.php
index d5acb1c931b1..2c1500942b9e 100644
--- a/lib/filestorage/tests/file_storage_test.php
+++ b/lib/filestorage/tests/file_storage_test.php
@@ -540,7 +540,7 @@ private function setup_three_private_files() {
      *
      * @covers ::get_area_files
      */
-    public function test_get_area_files() {
+    public function test_get_area_files(): void {
         $user = $this->setup_three_private_files();
         $fs = get_file_storage();
 
diff --git a/lib/form/tests/filetypes_util_test.php b/lib/form/tests/filetypes_util_test.php
index d932964423f3..f1cd3d5f7c7f 100644
--- a/lib/form/tests/filetypes_util_test.php
+++ b/lib/form/tests/filetypes_util_test.php
@@ -273,7 +273,7 @@ public function test_get_not_listed(): void {
     /**
      * Test populating the tree for the browser.
      */
-    public function test_data_for_browser() {
+    public function test_data_for_browser(): void {
 
         $this->resetAfterTest(true);
         $util = new filetypes_util();
diff --git a/lib/phpunit/tests/phpunit_dataset_test.php b/lib/phpunit/tests/phpunit_dataset_test.php
index c0c1cd64d6f6..56dc9a29cc0f 100644
--- a/lib/phpunit/tests/phpunit_dataset_test.php
+++ b/lib/phpunit/tests/phpunit_dataset_test.php
@@ -771,7 +771,7 @@ public function to_database_provider() {
      * @dataProvider to_database_provider
      * @covers ::to_database
      */
-    public function test_to_database(array $files, ?array $filter, ?string $exception, array $columns, array $rows) {
+    public function test_to_database(array $files, ?array $filter, ?string $exception, array $columns, array $rows): void {
         global $DB;
 
         $this->resetAfterTest();
diff --git a/lib/tests/authlib_test.php b/lib/tests/authlib_test.php
index 1e02010f7eda..cb649428f1da 100644
--- a/lib/tests/authlib_test.php
+++ b/lib/tests/authlib_test.php
@@ -448,7 +448,7 @@ public function test_user_loggedin_event_exceptions(): void {
     /**
      * Test the {@link signup_validate_data()} duplicate email validation.
      */
-    public function test_signup_validate_data_same_email() {
+    public function test_signup_validate_data_same_email(): void {
         global $CFG;
         require_once($CFG->libdir . '/authlib.php');
         require_once($CFG->libdir . '/phpmailer/moodle_phpmailer.php');
diff --git a/lib/tests/core_media_player_native_test.php b/lib/tests/core_media_player_native_test.php
index 6d563f47c20a..5841c4bbbfec 100644
--- a/lib/tests/core_media_player_native_test.php
+++ b/lib/tests/core_media_player_native_test.php
@@ -58,7 +58,7 @@ public function test_get_supported_extensions(): void {
     /**
      * Test method list_supported_urls
      */
-    public function test_list_supported_urls() {
+    public function test_list_supported_urls(): void {
         global $CFG;
         require_once($CFG->libdir . '/filelib.php');
         $nativeextensions = file_get_typegroup('extension', ['html_video', 'html_audio']);
diff --git a/lib/tests/curl_security_helper_test.php b/lib/tests/curl_security_helper_test.php
index 3d92e9f588b7..568ff290d9fa 100644
--- a/lib/tests/curl_security_helper_test.php
+++ b/lib/tests/curl_security_helper_test.php
@@ -37,7 +37,7 @@ class curl_security_helper_test extends \advanced_testcase {
      * @param bool $expected the expected result.
      * @dataProvider curl_security_url_data_provider
      */
-    public function test_curl_security_helper_url_is_blocked($dns, $url, $blockedhosts, $allowedports, $expected) {
+    public function test_curl_security_helper_url_is_blocked($dns, $url, $blockedhosts, $allowedports, $expected): void {
         $this->resetAfterTest(true);
         $helper = $this->getMockBuilder('\core\files\curl_security_helper')
             ->onlyMethods(['get_host_list_by_name'])
diff --git a/lib/tests/grouplib_test.php b/lib/tests/grouplib_test.php
index ac363b42cc2f..b76bf7f9e38c 100644
--- a/lib/tests/grouplib_test.php
+++ b/lib/tests/grouplib_test.php
@@ -2050,7 +2050,7 @@ public function test_get_all_groups_with_visibility(): void {
      *
      * @covers \groups_get_my_groups()
      */
-    public function test_get_my_groups_with_visibility() {
+    public function test_get_my_groups_with_visibility(): void {
         list($users, $groups) = $this->create_groups_with_visibilty();
 
         // Assign users to groups.
diff --git a/lib/tests/navigation/output/primary_test.php b/lib/tests/navigation/output/primary_test.php
index 54e042c2ae16..25507be00665 100644
--- a/lib/tests/navigation/output/primary_test.php
+++ b/lib/tests/navigation/output/primary_test.php
@@ -54,7 +54,7 @@ public function setUp(): void {
      *                             otherwise consider the user as non-logged in
      * @param array $expecteditems An array of nodes expected with content in them.
      */
-    public function test_primary_export(bool $withcustom, bool $withlang, string $userloggedin, array $expecteditems) {
+    public function test_primary_export(bool $withcustom, bool $withlang, string $userloggedin, array $expecteditems): void {
         global $PAGE, $CFG;
         if ($withcustom) {
             $CFG->custommenuitems = "Course search|/course/search.php
diff --git a/lib/tests/output/mustache_helper_collection_test.php b/lib/tests/output/mustache_helper_collection_test.php
index 049225e907c2..296bd0185ae1 100644
--- a/lib/tests/output/mustache_helper_collection_test.php
+++ b/lib/tests/output/mustache_helper_collection_test.php
@@ -140,7 +140,7 @@ public function test_strip_disallowed_helpers($disallowed, $input, $expected): v
      * Any allowed helper should still be available to call during the
      * execution of a helper.
      */
-    public function test_disallowed_helpers_disabled_during_execution() {
+    public function test_disallowed_helpers_disabled_during_execution(): void {
         $engine = new \Mustache_Engine();
         $context = new \Mustache_Context();
         $lambdahelper = new \Mustache_LambdaHelper($engine, $context);
diff --git a/lib/tests/questionlib_test.php b/lib/tests/questionlib_test.php
index d4a7e07273f4..fa362c262211 100644
--- a/lib/tests/questionlib_test.php
+++ b/lib/tests/questionlib_test.php
@@ -695,7 +695,7 @@ public function test_get_question_options_course_tags_in_course_question_context
      * get_question_options includes the tags and course tags for all questions in the list
      * if each question has course and question level tags.
      */
-    public function test_get_question_options_includes_question_and_course_tags() {
+    public function test_get_question_options_includes_question_and_course_tags(): void {
         list($category, $course, $quiz, $qcat, $questions) = $this->setup_quiz_and_questions('category');
         $question1 = $questions[0];
         $question2 = $questions[1];
diff --git a/lib/tests/task/database_logger_test.php b/lib/tests/task/database_logger_test.php
index 1a0261332d43..80588bf2fd29 100644
--- a/lib/tests/task/database_logger_test.php
+++ b/lib/tests/task/database_logger_test.php
@@ -212,7 +212,7 @@ public function test_store_log_for_task_adhoc_userid(): void {
      * @dataProvider    delete_task_logs_provider
      * @param   mixed   $ids
      */
-    public function test_delete_task_logs($ids) {
+    public function test_delete_task_logs($ids): void {
         $DB = $this->mock_database();
         $DB->expects($this->once())
             ->method('delete_records_list')
diff --git a/login/tests/login_lib_test.php b/login/tests/login_lib_test.php
index bdafdf7a1d96..2cab15a41740 100644
--- a/login/tests/login_lib_test.php
+++ b/login/tests/login_lib_test.php
@@ -383,7 +383,7 @@ public function test_core_login_validate_forgot_password_data($data, $errors = [
      *
      * Email addresses should be handled as case-insensitive but accent sensitive.
      */
-    public function test_core_login_process_password_reset_email_sensitivity() {
+    public function test_core_login_process_password_reset_email_sensitivity(): void {
         global $CFG;
         require_once($CFG->libdir.'/phpmailer/moodle_phpmailer.php');
 
diff --git a/media/player/html5audio/tests/player_test.php b/media/player/html5audio/tests/player_test.php
index da8bd0056152..2650ab06905d 100644
--- a/media/player/html5audio/tests/player_test.php
+++ b/media/player/html5audio/tests/player_test.php
@@ -70,7 +70,7 @@ public function test_get_supported_extensions(): void {
     /**
      * Test method list_supported_urls()
      */
-    public function test_list_supported_urls() {
+    public function test_list_supported_urls(): void {
         global $CFG;
         require_once($CFG->libdir . '/filelib.php');
 
diff --git a/media/player/html5video/tests/player_test.php b/media/player/html5video/tests/player_test.php
index 66aaf731e5d0..98ee415ca842 100644
--- a/media/player/html5video/tests/player_test.php
+++ b/media/player/html5video/tests/player_test.php
@@ -67,7 +67,7 @@ public function test_get_supported_extensions(): void {
     /**
      * Test method list_supported_urls()
      */
-    public function test_list_supported_urls() {
+    public function test_list_supported_urls(): void {
         global $CFG;
         require_once($CFG->libdir . '/filelib.php');
 
diff --git a/message/tests/api_test.php b/message/tests/api_test.php
index cceae4fa6639..b5801e8e492f 100644
--- a/message/tests/api_test.php
+++ b/message/tests/api_test.php
@@ -1277,7 +1277,7 @@ public function test_get_conversations_message_format(): void {
     /**
      * Test verifying get_conversations identifies if a conversation is muted or not.
      */
-    public function test_get_conversations_some_muted() {
+    public function test_get_conversations_some_muted(): void {
         // Create some users.
         $user1 = self::getDataGenerator()->create_user();
         $user2 = self::getDataGenerator()->create_user();
@@ -5749,7 +5749,7 @@ public function test_get_conversation_counts(
         $expectedcounts,
         $expectedunreadcounts,
         $deletedusers
-    ) {
+    ): void {
         $generator = $this->getDataGenerator();
         $users = [
             $generator->create_user(),
@@ -5872,7 +5872,7 @@ public function test_get_unread_conversation_counts(
         $expectedcounts,
         $expectedunreadcounts,
         $deletedusers
-    ) {
+    ): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
         $users = [
diff --git a/message/tests/externallib_test.php b/message/tests/externallib_test.php
index a4b6f7f72fe3..6769c630c8ac 100644
--- a/message/tests/externallib_test.php
+++ b/message/tests/externallib_test.php
@@ -2032,7 +2032,7 @@ public function test_get_user_notification_preferences_permissions(): void {
      * If checks this by placing some users in the same course, where default caps would permit a user to view another user's
      * profile.
      */
-    public function test_message_search_users_messagingallusers_disabled() {
+    public function test_message_search_users_messagingallusers_disabled(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -2128,7 +2128,7 @@ public function test_message_search_users_messagingallusers_disabled() {
      * This test verifies that any contacts are returned, as well as any non-contacts, regardless of whether the searching user
      * can view their respective profile.
      */
-    public function test_message_search_users_messagingallusers_enabled() {
+    public function test_message_search_users_messagingallusers_enabled(): void {
         global $DB;
         $this->resetAfterTest();
 
@@ -4395,7 +4395,7 @@ public function test_get_conversations_user_in_group_and_individual_chat(): void
     /**
      * Test verifying get_conversations identifies if a conversation is muted or not.
      */
-    public function test_get_conversations_some_muted() {
+    public function test_get_conversations_some_muted(): void {
         $this->resetAfterTest();
 
         // Create some users.
@@ -5518,7 +5518,7 @@ public function test_get_conversation_counts(
         $expectedcounts,
         $expectedunreadcounts,
         $deletedusers
-    ) {
+    ): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
         $users = [
@@ -5615,7 +5615,7 @@ public function test_get_unread_conversation_counts(
         $expectedcounts,
         $expectedunreadcounts,
         $deletedusers
-    ) {
+    ): void {
         $this->resetAfterTest();
         $generator = $this->getDataGenerator();
         $users = [
diff --git a/message/tests/privacy/provider_test.php b/message/tests/privacy/provider_test.php
index f3f6c8f82fbc..8f8cb4a6a7da 100644
--- a/message/tests/privacy/provider_test.php
+++ b/message/tests/privacy/provider_test.php
@@ -1048,7 +1048,7 @@ public function test_delete_data_for_all_users_in_context(): void {
     /**
      * Test for provider::delete_data_for_user().
      */
-    public function test_delete_data_for_user() {
+    public function test_delete_data_for_user(): void {
         global $DB;
 
         $this->resetAfterTest();
@@ -1382,7 +1382,7 @@ public function test_get_users_in_context_with_blocked_contact(): void {
     /**
      * Test for provider::delete_data_for_users().
      */
-    public function test_delete_data_for_users() {
+    public function test_delete_data_for_users(): void {
         global $DB;
 
         $this->resetAfterTest();
@@ -1866,7 +1866,7 @@ public function test_export_conversations(): void {
     /**
      * Test for provider::delete_conversations_for_all_users().
      */
-    public function test_delete_conversations_for_all_users() {
+    public function test_delete_conversations_for_all_users(): void {
         global $DB;
 
         $this->resetAfterTest();
@@ -2391,7 +2391,7 @@ public function test_delete_conversations_for_all_users_usercontext(): void {
     /**
      * Test for provider::delete_conversations_for_user().
      */
-    public function test_delete_conversations_for_user() {
+    public function test_delete_conversations_for_user(): void {
         global $DB;
 
         $this->resetAfterTest();
@@ -2589,7 +2589,7 @@ public function test_delete_conversations_for_user() {
     /**
      * Test for provider::delete_conversations_for_users().
      */
-    public function test_delete_conversations_for_users() {
+    public function test_delete_conversations_for_users(): void {
         global $DB;
 
         $this->resetAfterTest();
diff --git a/mod/assign/tests/external/start_submission_test.php b/mod/assign/tests/external/start_submission_test.php
index 2394ceaf9fc6..682d7d221631 100644
--- a/mod/assign/tests/external/start_submission_test.php
+++ b/mod/assign/tests/external/start_submission_test.php
@@ -69,7 +69,7 @@ public function test_start_submission_when_user_has_no_capability_to_view_assign
     /**
      * Test start_submission if assignment cut off date has elapsed.
      */
-    public function test_start_submission_when_assignment_past_due_date() {
+    public function test_start_submission_when_assignment_past_due_date(): void {
         $fiveminago = time() - 300;
         list($assign, $instance, $student1, $student2, $teacher, $g1, $g2) = $this->create_submission_for_testing_status(
                 false, ['cutoffdate' => $fiveminago]);
@@ -87,7 +87,7 @@ public function test_start_submission_when_assignment_past_due_date() {
     /**
      * Test start_submission if time limit is disabled.
      */
-    public function test_start_submission_when_time_limit_disabled() {
+    public function test_start_submission_when_time_limit_disabled(): void {
         list($assign, $instance, $student1, $student2, $teacher, $g1, $g2) = $this->create_submission_for_testing_status();
         $result = start_submission::execute($instance->id);
         $filteredwarnings = array_filter($result['warnings'], function($warning) {
@@ -103,7 +103,7 @@ public function test_start_submission_when_time_limit_disabled() {
     /**
      * Test start_submission if time limit is not set for assignment.
      */
-    public function test_start_submission_when_time_limit_not_set() {
+    public function test_start_submission_when_time_limit_not_set(): void {
         set_config('enabletimelimit', '1', 'assign');
         list($assign, $instance, $student1, $student2, $teacher, $g1, $g2) = $this->create_submission_for_testing_status();
         $result = start_submission::execute($instance->id);
@@ -120,7 +120,7 @@ public function test_start_submission_when_time_limit_not_set() {
     /**
      * Test start_submission if user already has open submission.
      */
-    public function test_start_submission_when_submission_already_open() {
+    public function test_start_submission_when_submission_already_open(): void {
         global $DB;
         set_config('enabletimelimit', '1', 'assign');
         list($assign, $instance, $student1, $student2, $teacher, $g1, $g2) = $this->create_submission_for_testing_status(
@@ -142,7 +142,7 @@ public function test_start_submission_when_submission_already_open() {
     /**
      * Test start_submission if user has already submitted with no additional attempts available.
      */
-    public function test_start_submission_with_no_attempts_available() {
+    public function test_start_submission_with_no_attempts_available(): void {
         global $DB;
         set_config('enabletimelimit', '1', 'assign');
         list($assign, $instance, $student1, $student2, $teacher, $g1, $g2) = $this->create_submission_for_testing_status(
diff --git a/mod/assign/tests/externallib_test.php b/mod/assign/tests/externallib_test.php
index 7919f6bab418..1e519aba23e2 100644
--- a/mod/assign/tests/externallib_test.php
+++ b/mod/assign/tests/externallib_test.php
@@ -332,7 +332,7 @@ public function test_get_assignments(): void {
     /**
      * Test get_assignments with submissionstatement.
      */
-    public function test_get_assignments_with_submissionstatement() {
+    public function test_get_assignments_with_submissionstatement(): void {
         global $DB, $USER, $CFG;
 
         $this->resetAfterTest(true);
diff --git a/mod/assign/tests/lib_test.php b/mod/assign/tests/lib_test.php
index 42ffbeca3ece..a07412c540d4 100644
--- a/mod/assign/tests/lib_test.php
+++ b/mod/assign/tests/lib_test.php
@@ -1377,7 +1377,7 @@ public function test_student_role_cant_update_due_event(): void {
      * able to update the assignment due date by changing the due date calendar
      * event.
      */
-    public function test_teacher_role_can_update_due_event() {
+    public function test_teacher_role_can_update_due_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . '/calendar/lib.php');
 
diff --git a/mod/bigbluebuttonbn/tests/external/get_recordings_test.php b/mod/bigbluebuttonbn/tests/external/get_recordings_test.php
index 556c894d3be0..ddda640e7cdf 100644
--- a/mod/bigbluebuttonbn/tests/external/get_recordings_test.php
+++ b/mod/bigbluebuttonbn/tests/external/get_recordings_test.php
@@ -379,7 +379,7 @@ public function test_get_imported_recordings_only(): void {
      * @covers   \mod_bigbluebuttonbn\external\get_recordings::execute
      * @dataProvider recording_group_test_data
      */
-    public function test_get_recordings_groups($type, $groups, $users, $recordingsdata, $test, $coursemode) {
+    public function test_get_recordings_groups($type, $groups, $users, $recordingsdata, $test, $coursemode): void {
         $this->resetAfterTest();
         $dataset = compact('type', 'groups', 'users', 'recordingsdata', 'test', 'coursemode');
         $activityid = $this->create_from_dataset($dataset);
diff --git a/mod/bigbluebuttonbn/tests/lib_test.php b/mod/bigbluebuttonbn/tests/lib_test.php
index 166ee95bd191..1fb00a50bd5c 100644
--- a/mod/bigbluebuttonbn/tests/lib_test.php
+++ b/mod/bigbluebuttonbn/tests/lib_test.php
@@ -130,7 +130,7 @@ public function test_bigbluebuttonbn_delete_instance_with_running_meeting(): voi
      *
      * @covers ::bigbluebuttonbn_delete_instance
      */
-    public function test_bigbluebuttonbn_delete_instance_with_running_group_meetings() {
+    public function test_bigbluebuttonbn_delete_instance_with_running_group_meetings(): void {
         $this->resetAfterTest();
         $this->initialise_mock_server();
         $datagenerator = $this->getDataGenerator();
@@ -224,7 +224,7 @@ public function test_bigbluebuttonbn_user_complete(): void {
      *
      * @covers ::bigbluebuttonbn_get_recent_mod_activity
      */
-    public function test_bigbluebuttonbn_get_recent_mod_activity() {
+    public function test_bigbluebuttonbn_get_recent_mod_activity(): void {
         $this->initialise_mock_server();
         $this->resetAfterTest();
 
diff --git a/mod/bigbluebuttonbn/tests/local/proxy/recording_proxy_test.php b/mod/bigbluebuttonbn/tests/local/proxy/recording_proxy_test.php
index e50dd4a1c0ec..829597a91465 100644
--- a/mod/bigbluebuttonbn/tests/local/proxy/recording_proxy_test.php
+++ b/mod/bigbluebuttonbn/tests/local/proxy/recording_proxy_test.php
@@ -37,7 +37,7 @@ class recording_proxy_test extends \advanced_testcase {
      *
      * @return void
      */
-    public function test_fetch_recordings() {
+    public function test_fetch_recordings(): void {
         $this->resetAfterTest();
         $this->initialise_mock_server();
         [$context, $cm, $bbbactivity] = $this->create_instance();
@@ -55,7 +55,7 @@ public function test_fetch_recordings() {
      *
      * @return void
      */
-    public function test_fetch_recordings_breakoutroom() {
+    public function test_fetch_recordings_breakoutroom(): void {
         $this->resetAfterTest();
         $this->initialise_mock_server();
         [$context, $cm, $bbbactivity] = $this->create_instance();
diff --git a/mod/bigbluebuttonbn/tests/output/recording_row_playback_test.php b/mod/bigbluebuttonbn/tests/output/recording_row_playback_test.php
index 510a789c6047..2c859d778ec7 100644
--- a/mod/bigbluebuttonbn/tests/output/recording_row_playback_test.php
+++ b/mod/bigbluebuttonbn/tests/output/recording_row_playback_test.php
@@ -95,7 +95,7 @@ public function setUp(): void {
      * @covers       \recording_row_playback::should_be_included
      * @dataProvider should_be_included_data_provider
      */
-    public function test_should_be_included(string $role, array $canview, object $globalsettings = null) {
+    public function test_should_be_included(string $role, array $canview, object $globalsettings = null): void {
         global $PAGE;
         $this->resetAfterTest();
         ['recordings' => $recordingsdata, 'activity' => $activity] = $this->create_activity_with_recordings(
diff --git a/mod/choice/tests/lib_test.php b/mod/choice/tests/lib_test.php
index a5a7108db7ac..9cd5eecf49f4 100644
--- a/mod/choice/tests/lib_test.php
+++ b/mod/choice/tests/lib_test.php
@@ -889,7 +889,7 @@ public function test_mod_choice_core_calendar_event_timestart_updated_unknown_ev
      * A CHOICE_EVENT_TYPE_OPEN event should update the timeopen property of
      * the choice activity.
      */
-    public function test_mod_choice_core_calendar_event_timestart_updated_open_event() {
+    public function test_mod_choice_core_calendar_event_timestart_updated_open_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . "/calendar/lib.php");
 
@@ -950,7 +950,7 @@ public function test_mod_choice_core_calendar_event_timestart_updated_open_event
      * A CHOICE_EVENT_TYPE_CLOSE event should update the timeclose property of
      * the choice activity.
      */
-    public function test_mod_choice_core_calendar_event_timestart_updated_close_event() {
+    public function test_mod_choice_core_calendar_event_timestart_updated_close_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . "/calendar/lib.php");
 
diff --git a/mod/data/tests/lib_test.php b/mod/data/tests/lib_test.php
index 1e4c7a45ff10..15b194289972 100644
--- a/mod/data/tests/lib_test.php
+++ b/mod/data/tests/lib_test.php
@@ -1706,7 +1706,7 @@ public function test_mod_data_core_calendar_event_timestart_updated_unknown_even
     /**
      * A DATA_EVENT_TYPE_OPEN event should update the timeavailablefrom property of the data activity.
      */
-    public function test_mod_data_core_calendar_event_timestart_updated_open_event() {
+    public function test_mod_data_core_calendar_event_timestart_updated_open_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . "/calendar/lib.php");
 
@@ -1763,7 +1763,7 @@ public function test_mod_data_core_calendar_event_timestart_updated_open_event()
     /**
      * A DATA_EVENT_TYPE_CLOSE event should update the timeavailableto property of the data activity.
      */
-    public function test_mod_data_core_calendar_event_timestart_updated_close_event() {
+    public function test_mod_data_core_calendar_event_timestart_updated_close_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . "/calendar/lib.php");
 
diff --git a/mod/data/tests/manager_test.php b/mod/data/tests/manager_test.php
index 65d829a1109a..3fae83e2d86e 100644
--- a/mod/data/tests/manager_test.php
+++ b/mod/data/tests/manager_test.php
@@ -222,7 +222,7 @@ public function test_has_fields(): void {
      *
      * @covers ::get_available_presets
      */
-    public function test_get_available_presets() {
+    public function test_get_available_presets(): void {
         global $DB;
 
         $this->resetAfterTest();
@@ -323,7 +323,7 @@ public function test_get_available_presets() {
      *
      * @covers ::get_available_plugin_presets
      */
-    public function test_get_available_plugin_presets() {
+    public function test_get_available_plugin_presets(): void {
         $this->resetAfterTest();
         $this->setAdminUser();
 
@@ -369,7 +369,7 @@ public function test_get_available_plugin_presets() {
      *
      * @covers ::get_available_saved_presets
      */
-    public function test_get_available_saved_presets() {
+    public function test_get_available_saved_presets(): void {
         global $DB;
 
         $this->resetAfterTest();
diff --git a/mod/data/tests/preset_test.php b/mod/data/tests/preset_test.php
index 4df4c3b38feb..163bfd09545a 100644
--- a/mod/data/tests/preset_test.php
+++ b/mod/data/tests/preset_test.php
@@ -208,7 +208,7 @@ public function test_create_from_fullname(): void {
      *
      * @covers ::save
      */
-    public function test_save_new_preset() {
+    public function test_save_new_preset(): void {
         $this->resetAfterTest();
         $this->setAdminUser();
 
diff --git a/mod/feedback/tests/lib_test.php b/mod/feedback/tests/lib_test.php
index ebddb43138c9..0656b3fc2f1b 100644
--- a/mod/feedback/tests/lib_test.php
+++ b/mod/feedback/tests/lib_test.php
@@ -1076,7 +1076,7 @@ public function test_student_role_cant_update_time_close_event(): void {
      * The activity should update if a teacher modifies the calendar
      * event.
      */
-    public function test_teacher_role_can_update_time_close_event() {
+    public function test_teacher_role_can_update_time_close_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . '/calendar/lib.php');
 
diff --git a/mod/forum/tests/builders_exported_posts_test.php b/mod/forum/tests/builders_exported_posts_test.php
index c8822db5fd57..fd88c64363a4 100644
--- a/mod/forum/tests/builders_exported_posts_test.php
+++ b/mod/forum/tests/builders_exported_posts_test.php
@@ -142,7 +142,7 @@ public function test_build_throws_exception_on_missing_discussions(): void {
      * Test the build function returns the exported posts in the order that the posts are
      * given.
      */
-    public function test_build_returns_posts_in_order() {
+    public function test_build_returns_posts_in_order(): void {
         $this->resetAfterTest();
 
         $datagenerator = $this->getDataGenerator();
@@ -185,7 +185,7 @@ public function test_build_returns_posts_in_order() {
     /**
      * Test the build function loads authors.
      */
-    public function test_build_loads_authors() {
+    public function test_build_loads_authors(): void {
         $this->resetAfterTest();
 
         $datagenerator = $this->getDataGenerator();
@@ -230,7 +230,7 @@ public function test_build_loads_authors() {
     /**
      * Test the build function loads attachments.
      */
-    public function test_build_loads_attachments() {
+    public function test_build_loads_attachments(): void {
         $this->resetAfterTest();
 
         $datagenerator = $this->getDataGenerator();
@@ -306,7 +306,7 @@ public function test_build_loads_attachments() {
     /**
      * Test the build function loads author groups.
      */
-    public function test_build_loads_author_groups() {
+    public function test_build_loads_author_groups(): void {
         $this->resetAfterTest();
 
         $datagenerator = $this->getDataGenerator();
@@ -376,7 +376,7 @@ public function test_build_loads_author_groups() {
     /**
      * Test the build function loads tags.
      */
-    public function test_build_loads_tags() {
+    public function test_build_loads_tags(): void {
         $this->resetAfterTest();
 
         $datagenerator = $this->getDataGenerator();
@@ -437,7 +437,7 @@ public function test_build_loads_tags() {
     /**
      * Test the build function loads read_receipts.
      */
-    public function test_build_loads_read_receipts() {
+    public function test_build_loads_read_receipts(): void {
         $this->resetAfterTest();
 
         $datagenerator = $this->getDataGenerator();
diff --git a/mod/forum/tests/entities_sorter_test.php b/mod/forum/tests/entities_sorter_test.php
index 28e32e285a60..62b4697fcf28 100644
--- a/mod/forum/tests/entities_sorter_test.php
+++ b/mod/forum/tests/entities_sorter_test.php
@@ -29,7 +29,7 @@ class entities_sorter_test extends \advanced_testcase {
     /**
      * Test the entity returns expected values.
      */
-    public function test_entity_sort_into_children() {
+    public function test_entity_sort_into_children(): void {
         $this->resetAfterTest();
         $sorter = new sorter_entity(
             function($entity) {
@@ -59,7 +59,7 @@ function($entity) {
     /**
      * Test the entity returns expected values.
      */
-    public function test_entity_flatten_children() {
+    public function test_entity_flatten_children(): void {
         $this->resetAfterTest();
         $sorter = new sorter_entity(
             function($entity) {
diff --git a/mod/forum/tests/privacy/provider_test.php b/mod/forum/tests/privacy/provider_test.php
index 0e47f7fefd66..11f18124b65c 100644
--- a/mod/forum/tests/privacy/provider_test.php
+++ b/mod/forum/tests/privacy/provider_test.php
@@ -1063,7 +1063,7 @@ public function test_post_tags(): void {
     /**
      * Ensure that all user data is deleted from a context.
      */
-    public function test_all_users_deleted_from_context() {
+    public function test_all_users_deleted_from_context(): void {
         global $DB;
 
         $fs = get_file_storage();
@@ -1268,7 +1268,7 @@ public function test_all_users_deleted_from_context() {
     /**
      * Ensure that all user data is deleted for a specific context.
      */
-    public function test_delete_data_for_user() {
+    public function test_delete_data_for_user(): void {
         global $DB;
 
         $fs = get_file_storage();
@@ -1483,7 +1483,7 @@ public function test_delete_data_for_user() {
     /**
      * Ensure that user data for specific users is deleted from a specified context.
      */
-    public function test_delete_data_for_users() {
+    public function test_delete_data_for_users(): void {
         global $DB;
 
         $fs = get_file_storage();
diff --git a/mod/forum/tests/vaults_forum_test.php b/mod/forum/tests/vaults_forum_test.php
index 71b1210fccd8..e240764f6e63 100644
--- a/mod/forum/tests/vaults_forum_test.php
+++ b/mod/forum/tests/vaults_forum_test.php
@@ -85,7 +85,7 @@ public function test_get_from_course_module_id(): void {
      *
      * @covers ::get_from_course_module_ids
      */
-    public function test_get_from_course_module_ids() {
+    public function test_get_from_course_module_ids(): void {
         $this->resetAfterTest();
 
         $vaultfactory = \mod_forum\local\container::get_vault_factory();
diff --git a/mod/h5pactivity/tests/external/get_h5pactivities_by_courses_test.php b/mod/h5pactivity/tests/external/get_h5pactivities_by_courses_test.php
index 17e80c82bfc7..33908fccfa5f 100644
--- a/mod/h5pactivity/tests/external/get_h5pactivities_by_courses_test.php
+++ b/mod/h5pactivity/tests/external/get_h5pactivities_by_courses_test.php
@@ -48,7 +48,7 @@ class get_h5pactivities_by_courses_test extends externallib_advanced_testcase {
     /**
      * Test test_get_h5pactivities_by_courses user student.
      */
-    public function test_get_h5pactivities_by_courses() {
+    public function test_get_h5pactivities_by_courses(): void {
         global $CFG, $DB;
 
         $this->resetAfterTest();
diff --git a/mod/lesson/tests/lib_test.php b/mod/lesson/tests/lib_test.php
index 17a2e63ea76b..0f6e6406fc6d 100644
--- a/mod/lesson/tests/lib_test.php
+++ b/mod/lesson/tests/lib_test.php
@@ -827,7 +827,7 @@ public function test_mod_lesson_core_calendar_event_timestart_updated_unknown_ev
     /**
      * A LESSON_EVENT_TYPE_OPEN event should update the available property of the lesson activity.
      */
-    public function test_mod_lesson_core_calendar_event_timestart_updated_open_event() {
+    public function test_mod_lesson_core_calendar_event_timestart_updated_open_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . "/calendar/lib.php");
 
@@ -887,7 +887,7 @@ public function test_mod_lesson_core_calendar_event_timestart_updated_open_event
     /**
      * A LESSON_EVENT_TYPE_CLOSE event should update the deadline property of the lesson activity.
      */
-    public function test_mod_lesson_core_calendar_event_timestart_updated_close_event() {
+    public function test_mod_lesson_core_calendar_event_timestart_updated_close_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . "/calendar/lib.php");
         $this->resetAfterTest(true);
diff --git a/mod/quiz/tests/calendar_event_modified_test.php b/mod/quiz/tests/calendar_event_modified_test.php
index 5e52b2774350..6caf143da6b3 100644
--- a/mod/quiz/tests/calendar_event_modified_test.php
+++ b/mod/quiz/tests/calendar_event_modified_test.php
@@ -273,7 +273,7 @@ public function test_student_role_cant_update_quiz_activity(): void {
      * able to update the quiz activity dates by changing the calendar
      * event.
      */
-    public function test_teacher_role_can_update_quiz_activity() {
+    public function test_teacher_role_can_update_quiz_activity(): void {
         global $DB;
 
         $this->resetAfterTest();
diff --git a/mod/quiz/tests/local_structure_slot_random_test.php b/mod/quiz/tests/local_structure_slot_random_test.php
index 039f159cea99..dd2a764ad4f6 100644
--- a/mod/quiz/tests/local_structure_slot_random_test.php
+++ b/mod/quiz/tests/local_structure_slot_random_test.php
@@ -226,7 +226,7 @@ public function test_set_tags_filter(): void {
             (array)json_decode($tagspropery)->filters->qtagids->values);
     }
 
-    public function test_insert() {
+    public function test_insert(): void {
         global $SITE;
 
         $this->resetAfterTest();
diff --git a/mod/scorm/tests/externallib_test.php b/mod/scorm/tests/externallib_test.php
index c365adfdea54..3f7fbc5fa0aa 100644
--- a/mod/scorm/tests/externallib_test.php
+++ b/mod/scorm/tests/externallib_test.php
@@ -227,7 +227,7 @@ public function test_mod_scorm_get_scorm_attempt_count_invalid_userid(): void {
     /**
      * Test get scorm scoes
      */
-    public function test_mod_scorm_get_scorm_scoes() {
+    public function test_mod_scorm_get_scorm_scoes(): void {
         global $DB;
 
         $this->resetAfterTest(true);
diff --git a/mod/scorm/tests/lib_test.php b/mod/scorm/tests/lib_test.php
index 8d85bad93d45..01fb3cd6d5ab 100644
--- a/mod/scorm/tests/lib_test.php
+++ b/mod/scorm/tests/lib_test.php
@@ -633,7 +633,7 @@ public function test_mod_scorm_core_calendar_event_timestart_updated_unknown_eve
      * A SCORM_EVENT_TYPE_OPEN event should update the timeopen property of
      * the scorm activity.
      */
-    public function test_mod_scorm_core_calendar_event_timestart_updated_open_event() {
+    public function test_mod_scorm_core_calendar_event_timestart_updated_open_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . "/calendar/lib.php");
 
@@ -694,7 +694,7 @@ public function test_mod_scorm_core_calendar_event_timestart_updated_open_event(
      * A SCORM_EVENT_TYPE_CLOSE event should update the timeclose property of
      * the scorm activity.
      */
-    public function test_mod_scorm_core_calendar_event_timestart_updated_close_event() {
+    public function test_mod_scorm_core_calendar_event_timestart_updated_close_event(): void {
         global $CFG, $DB;
         require_once($CFG->dirroot . "/calendar/lib.php");
 
diff --git a/mod/wiki/tests/privacy/provider_test.php b/mod/wiki/tests/privacy/provider_test.php
index e39ef8d3feb5..2a442027468f 100644
--- a/mod/wiki/tests/privacy/provider_test.php
+++ b/mod/wiki/tests/privacy/provider_test.php
@@ -327,7 +327,7 @@ public function test_get_users_in_context(): void {
     /**
      * Export data for user 1
      */
-    public function test_export_user_data1() {
+    public function test_export_user_data1(): void {
 
         // Export all contexts for the first user.
         $contextids = array_values(array_map(function($c) {
@@ -383,7 +383,7 @@ public function test_export_user_data1() {
     /**
      * Test export data for user 2
      */
-    public function test_export_user_data2() {
+    public function test_export_user_data2(): void {
 
         // Export all contexts for the second user.
         $contextids = array_values(array_map(function($c) {
@@ -434,7 +434,7 @@ public function test_export_user_data2() {
     /**
      * Test export data for user 3 (locks, empty individual wiki)
      */
-    public function test_export_user_data3() {
+    public function test_export_user_data3(): void {
 
         // Export all contexts for the third user.
         $contextids = array_values(array_map(function($c) {
@@ -515,7 +515,7 @@ protected function add_comment($page, $text) {
     /**
      * Test export data when there are comments.
      */
-    public function test_export_user_data_with_comments() {
+    public function test_export_user_data_with_comments(): void {
         global $DB;
         // Comment on each page in the first wiki as the first user.
         $this->setUser($this->users[1]);
diff --git a/privacy/tests/moodle_content_writer_test.php b/privacy/tests/moodle_content_writer_test.php
index 7b281a9ded7d..d718f70ca6cd 100644
--- a/privacy/tests/moodle_content_writer_test.php
+++ b/privacy/tests/moodle_content_writer_test.php
@@ -705,7 +705,7 @@ public function test_export_user_preference_context_block($component, $key, $val
      *
      * @covers ::export_user_preference
      */
-    public function test_export_user_preference_context_block_multiple_instances() {
+    public function test_export_user_preference_context_block_multiple_instances(): void {
         $this->resetAfterTest();
 
         $generator = $this->getDataGenerator();
@@ -1323,7 +1323,7 @@ public function rewrite_pluginfile_urls_provider() {
         ];
     }
 
-    public function test_export_html_functions() {
+    public function test_export_html_functions(): void {
         $this->resetAfterTest();
 
         $data = (object) ['key' => 'value'];
diff --git a/question/tests/externallib_test.php b/question/tests/externallib_test.php
index 002c87342713..f475cdd8dc46 100644
--- a/question/tests/externallib_test.php
+++ b/question/tests/externallib_test.php
@@ -195,7 +195,7 @@ public function test_get_random_question_summaries_variations(
         $includesubcategories,
         $usetagnames,
         $expectedquestionindexes
-    ) {
+    ): void {
         $this->resetAfterTest();
 
         $context = \context_system::instance();
@@ -365,7 +365,7 @@ public function test_get_random_question_summaries_formats_returned_questions():
     /**
      * get_random_question_summaries should allow limiting and offsetting of the result set.
      */
-    public function test_get_random_question_summaries_with_limit_and_offset() {
+    public function test_get_random_question_summaries_with_limit_and_offset(): void {
         $this->resetAfterTest();
         $numberofquestions = 5;
         $includesubcategories = false;
diff --git a/question/type/calculated/tests/question_type_test.php b/question/type/calculated/tests/question_type_test.php
index 271c60792b14..f638bcdb29e4 100644
--- a/question/type/calculated/tests/question_type_test.php
+++ b/question/type/calculated/tests/question_type_test.php
@@ -64,7 +64,7 @@ public function test_get_random_guess_score(): void {
         $this->assertEquals(0.1, $this->qtype->get_random_guess_score($q));
     }
 
-    public function test_load_question() {
+    public function test_load_question(): void {
         $this->resetAfterTest();
 
         $syscontext = \context_system::instance();
diff --git a/question/type/multianswer/tests/question_type_test.php b/question/type/multianswer/tests/question_type_test.php
index 34485048c64b..6cc5a6aba2e5 100644
--- a/question/type/multianswer/tests/question_type_test.php
+++ b/question/type/multianswer/tests/question_type_test.php
@@ -148,7 +148,7 @@ public function test_get_random_guess_score_with_all_missing_subquestions(): voi
         $this->assertNull($this->qtype->get_random_guess_score($questiondata));
     }
 
-    public function test_load_question() {
+    public function test_load_question(): void {
         $this->resetAfterTest();
 
         $syscontext = \context_system::instance();
diff --git a/repository/contentbank/tests/search/search_test.php b/repository/contentbank/tests/search/search_test.php
index 1ea14b9037f4..d2896bc2b155 100644
--- a/repository/contentbank/tests/search/search_test.php
+++ b/repository/contentbank/tests/search/search_test.php
@@ -47,7 +47,7 @@ class search_test extends \advanced_testcase {
      * @param string $search The search string
      * @param array $expected The array containing the expected content names that should be returned by the search
      */
-    public function test_get_search_contents(array $contentnames, string $search, array $expected) {
+    public function test_get_search_contents(array $contentnames, string $search, array $expected): void {
         $this->resetAfterTest();
 
         $admin = get_admin();
diff --git a/repository/dropbox/tests/api_test.php b/repository/dropbox/tests/api_test.php
index ea4360068785..6aec039ce13b 100644
--- a/repository/dropbox/tests/api_test.php
+++ b/repository/dropbox/tests/api_test.php
@@ -339,7 +339,7 @@ public function test_fetch_dropbox_data_endpoint(): void {
     /**
      * Some Dropbox endpoints require that the POSTFIELDS be set to null exactly.
      */
-    public function test_fetch_dropbox_data_postfields_null() {
+    public function test_fetch_dropbox_data_postfields_null(): void {
         $mock = $this->getMockBuilder(\repository_dropbox\dropbox::class)
             ->disableOriginalConstructor()
             ->onlyMethods([
@@ -365,7 +365,7 @@ public function test_fetch_dropbox_data_postfields_null() {
     /**
      * When data is specified, it should be json_encoded in POSTFIELDS.
      */
-    public function test_fetch_dropbox_data_postfields_data() {
+    public function test_fetch_dropbox_data_postfields_data(): void {
         $mock = $this->getMockBuilder(\repository_dropbox\dropbox::class)
             ->disableOriginalConstructor()
             ->onlyMethods([
@@ -442,7 +442,7 @@ public function test_fetch_dropbox_data_recurse_on_additional_records(): void {
     /**
      * Base tests for the fetch_dropbox_content function.
      */
-    public function test_fetch_dropbox_content() {
+    public function test_fetch_dropbox_content(): void {
         $mock = $this->getMockBuilder(\repository_dropbox\dropbox::class)
             ->disableOriginalConstructor()
             ->onlyMethods([
diff --git a/tag/tests/privacy/provider_test.php b/tag/tests/privacy/provider_test.php
index 5394d27b940c..a07b1bb56065 100644
--- a/tag/tests/privacy/provider_test.php
+++ b/tag/tests/privacy/provider_test.php
@@ -250,7 +250,7 @@ public function test_delete_data_for_all_users_in_context(): void {
         $this->assertEquals(0, $DB->count_records('tag_instance', []));
     }
 
-    public function test_export_data_for_user() {
+    public function test_export_data_for_user(): void {
         global $DB;
         list($user1, $user2) = $this->set_up_tags();
         $context = \context_system::instance();
diff --git a/tag/tests/taglib_test.php b/tag/tests/taglib_test.php
index 7a973515e7c9..96206f69bf45 100644
--- a/tag/tests/taglib_test.php
+++ b/tag/tests/taglib_test.php
@@ -325,7 +325,7 @@ protected function prepare_correlated() {
     /**
      * Test for function compute_correlations() that is part of tag cron
      */
-    public function test_correlations() {
+    public function test_correlations(): void {
         global $DB;
         $task = new \core\task\tag_cron_task();
 
@@ -929,7 +929,7 @@ public function test_combine_tags(): void {
     /**
      * Testing function core_tag_tag::combine_tags() when related tags are present.
      */
-    public function test_combine_tags_with_related() {
+    public function test_combine_tags_with_related(): void {
         $collid = core_tag_collection::get_default();
         $context = \context_system::instance();
         core_tag_tag::set_item_tags('core', 'course', 10, $context, array('Cat', 'Cats', 'Dog'));
@@ -1014,7 +1014,7 @@ public function test_get_tags_by_area_in_contexts_empty(): void {
      * have instances in the given context even when there is only a single
      * instance.
      */
-    public function test_get_tags_by_area_in_contexts_single_tag_one_context() {
+    public function test_get_tags_by_area_in_contexts_single_tag_one_context(): void {
         $tagnames = ['foo'];
         $collid = core_tag_collection::get_default();
         $tags = core_tag_tag::create_if_missing($collid, $tagnames);
@@ -1043,7 +1043,7 @@ public function test_get_tags_by_area_in_contexts_single_tag_one_context() {
      * that have tag instances in for the area in the given context and
      * should ignore all tags that don't have an instance.
      */
-    public function test_get_tags_by_area_in_contexts_multiple_tags_one_context() {
+    public function test_get_tags_by_area_in_contexts_multiple_tags_one_context(): void {
         $tagnames = ['foo', 'bar', 'baz'];
         $collid = core_tag_collection::get_default();
         $tags = core_tag_tag::create_if_missing($collid, $tagnames);
@@ -1073,7 +1073,7 @@ public function test_get_tags_by_area_in_contexts_multiple_tags_one_context() {
      * Tags with tag instances in the same area with in difference contexts
      * should be ignored.
      */
-    public function test_get_tags_by_area_in_contexts_multiple_tags_multiple_contexts() {
+    public function test_get_tags_by_area_in_contexts_multiple_tags_multiple_contexts(): void {
         $tagnames = ['foo', 'bar', 'baz', 'bop', 'bam', 'bip'];
         $collid = core_tag_collection::get_default();
         $tags = core_tag_tag::create_if_missing($collid, $tagnames);
@@ -1191,7 +1191,7 @@ public function test_get_items_tags_unknown_component_itemtype(): void {
      *      3 => []
      * ]
      */
-    public function test_get_items_tags_missing_itemids() {
+    public function test_get_items_tags_missing_itemids(): void {
         $user1 = $this->getDataGenerator()->create_user();
         $user2 = $this->getDataGenerator()->create_user();
         $user3 = $this->getDataGenerator()->create_user();
@@ -1232,7 +1232,7 @@ public function test_get_items_tags_missing_itemids() {
      * set_item_tags should remove any tags that aren't in the given list and should
      * add any instances that are missing.
      */
-    public function test_set_item_tags_no_multiple_context_add_remove_instances() {
+    public function test_set_item_tags_no_multiple_context_add_remove_instances(): void {
         $tagnames = ['foo', 'bar', 'baz', 'bop'];
         $collid = core_tag_collection::get_default();
         $tags = core_tag_tag::create_if_missing($collid, $tagnames);
@@ -1312,7 +1312,7 @@ public function test_set_item_tags_no_multiple_context_updates_context_of_instan
      * the new set of tags, regardless of the context that the tag instance
      * is in.
      */
-    public function test_set_item_tags_no_multiple_contex_deletes_old_instancest() {
+    public function test_set_item_tags_no_multiple_contex_deletes_old_instancest(): void {
         $tagnames = ['foo', 'bar', 'baz', 'bop'];
         $collid = core_tag_collection::get_default();
         $tags = core_tag_tag::create_if_missing($collid, $tagnames);
@@ -1361,7 +1361,7 @@ public function test_set_item_tags_no_multiple_contex_deletes_old_instancest() {
      * set_item_tags should not change tag instances in a different context to the one
      * it's opertating on if the tag area allows instances from multiple contexts.
      */
-    public function test_set_item_tags_allow_multiple_context_doesnt_update_context() {
+    public function test_set_item_tags_allow_multiple_context_doesnt_update_context(): void {
         global $DB;
         $tagnames = ['foo', 'bar', 'bop'];
         $collid = core_tag_collection::get_default();
@@ -1414,7 +1414,7 @@ public function test_set_item_tags_allow_multiple_context_doesnt_update_context(
      * the new set of tags only in the same context if the tag area allows
      * multiple contexts.
      */
-    public function test_set_item_tags_allow_multiple_context_deletes_instances_in_same_context() {
+    public function test_set_item_tags_allow_multiple_context_deletes_instances_in_same_context(): void {
         $tagnames = ['foo', 'bar', 'baz', 'bop'];
         $collid = core_tag_collection::get_default();
         $tags = core_tag_tag::create_if_missing($collid, $tagnames);
@@ -1458,7 +1458,7 @@ public function test_set_item_tags_allow_multiple_context_deletes_instances_in_s
      * set_item_tags should allow multiple instances of the same tag in different
      * contexts if the tag area allows multiple contexts.
      */
-    public function test_set_item_tags_allow_multiple_context_same_tag_multiple_contexts() {
+    public function test_set_item_tags_allow_multiple_context_same_tag_multiple_contexts(): void {
         $tagnames = ['foo'];
         $collid = core_tag_collection::get_default();
         $tags = core_tag_tag::create_if_missing($collid, $tagnames);
@@ -1788,7 +1788,7 @@ public function test_delete_instances_with_component_and_context(): void {
      * delete_instances should delete all tag instances for a component, item type
      * and context if given the component, itemtype, and context id as parameters.
      */
-    public function test_delete_instances_with_component_and_itemtype_and_context() {
+    public function test_delete_instances_with_component_and_itemtype_and_context(): void {
         global $DB;
 
         $tagnames = ['foo', 'bar', 'baz'];
diff --git a/user/tests/userlib_test.php b/user/tests/userlib_test.php
index bdb44dc87d39..9f5183717fde 100644
--- a/user/tests/userlib_test.php
+++ b/user/tests/userlib_test.php
@@ -984,7 +984,7 @@ public function test_user_get_user_details_permissions(): void {
      * Test user_get_user_details_groups.
      * @covers ::user_get_user_details
      */
-    public function test_user_get_user_details_groups() {
+    public function test_user_get_user_details_groups(): void {
         $this->resetAfterTest();
 
         // Create user and modify user profile.