It's common to create a base TestCase that defines some logic in setUp and tearDown methods of PHPUnit. Laravel, Symfony etc. does this.
So when a user is overriding the setUp or tearDown in a specific test class, forgetting to call parent::setUp() can cause some issues. (I got bitten by this today. Forgot to call parent::tearDown so database transactions were not committed. Apparently Laravel does this in it's tearDown)
It'd be good to have a rule that catches that. It should be a little smart about it, and only warn when parent setUp or tearDown is not the base PHPUnit TestCase.
If this is something that you see value in, I can try to implement it.