CONTRIBUTING.md

Contributing

Thank you for your interest in contributing to AssertJ!

We appreciate your effort and to make sure that your pull request is easy to review, we ask you to note the following guidelines including legal contributor agreement:

• Use AssertJ code Eclipse formatting preferences (for IntelliJ IDEA users, you can import it with the 'Eclipse Code Formatter' Plugin)

• Write complete Javadocs for each assertion method and include a code example (succeeding and failing assertion(s)).

• As we use JUnit 5, favor package-private visibility for both test classes and test methods.

• Write one JUnit test class for each assertion method with the following naming convention: <AssertClass>_<assertion>_Test.

• Use @DisplayName on the test class - see OptionalAssert_containsInstanceOf_Test as an example.

• Write unit test assertions with AssertJ! Let's eat our own dog food.

• Unit tests method naming convention is underscore-based (like python) and not camel-case, we find it is much readable for long test names!

• Successful assertion unit test method names should start with: should_pass_....

• Failing assertion unit test method names should start with: should_fail_....

• Put GIVEN WHEN THEN steps in each test, favoring BDDAssertions.then instead of Assertions.assertThat for assertions in the THEN step. Steps can be combined or omitted if a separate step does not provide much benefit to test readability, just ensure that the WHEN step (either single or combined) contains the test target.

• Use AssertionUtil.expectAssertionError for tests expecting to get an AssertionError - see OptionalAssert_containsInstanceOf_Test as an example..

• Use static import when it makes the code more readable.

• If possible, add a (fun) code example in assertj-examples and use it in the javadoc.

A good unit test to use as a reference is OptionalAssert_containsInstanceOf_Test. Here's a sample below:

import static org.assertj.core.api.BDDAssertions.then;
import static org.assertj.core.util.AssertionsUtil.expectAssertionError;
// other imports not shown for brevity

@DisplayName("OptionalAssert containsInstanceOf")
class OptionalAssert_containsInstanceOf_Test extends BaseTest {

  @Test
  void should_fail_if_optional_is_empty() {
    // GIVEN
    Optional<Object> actual = Optional.empty();
    // WHEN
    AssertionError assertionError = expectAssertionError(() -> assertThat(actual).containsInstanceOf(Object.class));
    // THEN
    then(assertionError).hasMessage(shouldBePresent(actual).create());
  }

  @Test
  void should_pass_if_optional_contains_required_type() {
    // GIVEN
    Optional<String> optional = Optional.of("something");
    // WHEN/THEN
    then(optional).containsInstanceOf(String.class);
  }

}

It's ok not to follow some of the rules described above if you have a good reason not to (use your best judgement)

assertj-examples shows how to efficiently use AssertJ through fun unit test examples, it can be seen as AssertJs living documentation.

Rebase your PR on main (no merge!)

We prefer integrating PR by squashing all the commits and rebase it to main, if you PR has diverged and needs to integrate with main, please rebase on main but do not merge as it will prevent rebasing later on.

Naming conventions with some examples:

Here some of ThrowableAssert assertions: hasMessage, hasNoCause, hasMessageContaining, for each of them we have a test class, note the naming convention:

• ThrowableAssert_hasMessage_Test
• ThrowableAssert_hasNoCause_Test
• ThrowableAssert_hasMessageContaining_Test

Let's look at Throwables_assertHasNoCause_Test tests method names (underscore based only):

• should_pass_if_actual_has_no_cause
• should_fail_if_actual_is_null
• should_fail_if_actual_has_a_cause

A good javadoc example taken from AbstractCharSequenceAssert.containsSequence including:

• assertion description
• a code example showing how to use the assertion (succeeding and failing assertion)
• parameters description (if any)
• exceptions description
• since tag (e.g. @since 3.9.0)

/**
 * Verifies that the actual {@code CharSequence} contains all the given strings <b>in the given order</b>.
 * <p>
 * Example:
 *
 * <pre><code class='java'> String book = "{ 'title':'A Game of Thrones', 'author':'George Martin'}";
 *
 * // this assertion succeeds ...
 * assertThat(book).containsSequence("{", "title", "A Game of Thrones", "}");
 *
 * // ... but this one fails as "author" must come after "A Game of Thrones"
 * assertThat(book).containsSequence("{", "author", "A Game of Thrones", "}"); </code></pre>
 *
 * @param values the Strings to look for, in order.
 * @return {@code this} assertion object.
 * @throws NullPointerException if the given values is {@code null}.
 * @throws IllegalArgumentException if the given values is empty.
 * @throws AssertionError if the actual {@code CharSequence} is {@code null}.
 * @throws AssertionError if the actual {@code CharSequence} does not contain all the given strings <b>in the given order</b>.
 * @since 2.1.0 / 3.1.0
 */

Legal stuff:

Project license(s): Apache License Version 2.0

As a contributor:

• You will only submit contributions where you have authored 100% of the content.
• You will only submit contributions to which you have the necessary rights. This means that if you are employed, you have received the necessary permissions from your employer to make the contributions.
• Whatever content you contribute will be provided under the project license(s).