Support Behat tests

[staabm]

Behat is a BDD framework for PHP to help you test business expectations.

Behat tests are written in classes which implement the Behat\Behat\Context\Context interface.

This PR adds the marker interface to the isTestClass utility function, which makes sure that BDD testing methods are taken into account like PHPUnit testing methods

• don't report tests as beeing only called locally
• detect application methods which are only called from with tests
• ...

[TomasVotruba]

Legit 👍 Thank you