Add tests to expose bug in appointment mail sending.

When a member schedules a new appointment with the same time as
an existing one, we merge the appointments together. However, we were still
sending an email with an appointment argument that was the appointment that
no longer existed after the merge. This led to deserialization errors when the
mail job was later processed.

test/controllers/account/appointments_controller_test.rb

@@ -20,6 +20,15 @@ class AppointmentsControllerTest < ActionDispatch::IntegrationTest
       @appointment.save
     end
 
+    private def assert_enqueued_email(mailer, method, params: {})
+      assert_enqueued_with(job: ActionMailer::MailDeliveryJob, args: ->(job_arguments) {
+        job_mailer, job_method, _delivery, rest = *job_arguments
+        assert_equal mailer.to_s, job_mailer
+        assert_equal method.to_s, job_method
+        assert_equal(params, rest[:params])
+      })
+    end
+
     test "creates a new appointment to pickup items on hold" do
       @hold = FactoryBot.create(:started_hold, member: @member)
       @event = FactoryBot.create(:appointment_slot_event)
@@ -30,6 +39,26 @@ class AppointmentsControllerTest < ActionDispatch::IntegrationTest
         time_range_string: "#{@event.start}..#{@event.finish}"
       }}
 
+      @appointment = @member.appointments.last
+      assert_enqueued_email(MemberMailer, :appointment_confirmation, params: {member: @member, appointment: @appointment})
+
+      assert_redirected_to account_appointments_path
+      assert_equal 1, @member.appointments.count
+    end
+
+    test "adds additional items to an existing appointment via creation form" do
+      create_appointment
+      @hold = FactoryBot.create(:started_hold, member: @member)
+
+      post account_appointments_path, params: {appointment: {
+        hold_ids: [@hold.id],
+        comment: "Excited to start on my project!",
+        time_range_string: "#{@appointment.starts_at}..#{@appointment.ends_at}"
+      }}
+
+      @appointment = @member.appointments.last
+      assert_enqueued_email(MemberMailer, :appointment_confirmation, params: {member: @member, appointment: @appointment})
+
       assert_redirected_to account_appointments_path
       assert_equal 1, @member.appointments.count
     end