--group option does not filter out test classes with no @group annotation

[ste93cry]

PHPUnit has a --group option that allows to specify which group of tests should be run. While Paratest has the same option, it behaves differently: it does not filter out test classes that do not have the @group annotation. Taking as example the code below (one class per file), I would expect that only the second test class is executed using the command vendor/bin/paratest --group=group1 while instead both are:

class FooTest extends \PHPUnit\Framework\TestCaseTestCase
{
}

/**
 * @group group1
 */
class BarTest extends \PHPUnit\Framework\TestCaseTestCase
{
}

Instead running plain PHPUnit using the command vendor/bin/phpunit --group=group1 works as expected. I tracked the error down to the SuiteLoader::testMatchGroupOptions method which returns true as long as no groups are defined on the test class. Even though I strongly believe that this is a bugfix, it also causes a huge BC. I'm willing to open PR to address the problem anyway, so let me know how we want to proceed

[Slamdunk]

Hi, a PR with the bugfix would be really appreciated. We'll take care of merging it according to an appropriate semver tag.