[Mailer] Add new email testing functions (fixes #50200)

JohJohan · JohJohan · commit ed4825d1ad8b · 2023-05-02T13:43:11.000+02:00
diff --git a/testing.rst b/testing.rst
@@ -1035,6 +1035,9 @@ Mailer Assertions
     Asserts that the given address header equals the expected e-mail
     address. This assertion normalizes addresses like ``Jane Smith
     <jane@example.com>`` into ``jane@example.com``.
+``assertEmailSubjectContains(RawMessage $email, string $expectedValue, string $message = '')``/``assertEmailSubjectNotContains(RawMessage $email, string $expectedValue, string $message = '')``
+    Asserts that the subject of the given email does (not) contain the
+    expected subject.
 
 Notifier Assertions
 ...................
