MinkTestCase::getKernel should be a static function as WebTestCase::createKernel is. The whole chain to get the kernel should be static as it's dealing with a static member of the class.
Otherwise calling getKernel from a static environment requires to use error suppression to suppress the warnings.
MinkTestCase::getKernelshould be a static function asWebTestCase::createKernelis. The whole chain to get the kernel should be static as it's dealing with a static member of the class. Otherwise callinggetKernelfrom a static environment requires to use error suppression to suppress the warnings.