Add @return void annotation to test methods (PoC)

Missing @return void annotation in phpdoc block of test methods lead to php codesniffer (phpcs) errors when using the TYPO3 CMS coding guidelines:

This function must always have a return value.
(TYPO3SniffPool.Scope.AlwaysReturn.AlwaysReturnStatement)

I suggest to add @return void annotations. Do you agree?