Problem/Motivation
Spin-off from #3063887: Support PHPUnit 8 in Drupal 9, drop support for PHPUnit 7.
PHPUnit 8 is changing the signature of the main test methods that test classes extend - above all setUp and tearDown, adding a void return typehint.
As per #3063887-75: Support PHPUnit 8 in Drupal 9, drop support for PHPUnit 7, in this issue we change the signatures of the methods in concrete Drupal test code according to PHPUnit 8.
Proposed resolution
Change all the implementations of
setUp()tearDown()setUpBeforeClass()assertPostConditions()
in concrete test classes to have a void return typehint.
We will then add a deprecation to inform developers of this change in #3111044: Deprecate setUp/tearDown concrete test methods that do not specify void return type
We cannot change abstract base test classes without breaking backward compatibility, so that will be done in a follow-up.
Remaining tasks
Patch.
User interface changes
API changes
Data model changes
Release notes snippet
Overridden test methods should have void return type hints added, see the change record at https://www.drupal.org/node/3114724 for more details.