allow TestBench usage without subclassing

[skiedrowski]

Enforcing subclassing of TestBenchTestCase makes integration in various contexts problematic.

If I would try to implement a Test using TestBench and another tool which forces subclassing of its own XyzTestCase, it would be impossible to use both.

UI Testing is just one aspect of a test, but very often not the only aspect.

JUnit 4 provides Rules, JUnit 5 provides Extensions and I guess TestNG also has a convenient way to integrate with multiple test libraries.

It would be great if Vaadin could provide a TestBenchRule for JUnit 4 and a TestBenchExtension for JUnit 5 if that would allow dropping the extends TestBenchTestCase.

[MarcinVaadin]

I'm currently on JUnit5 migration and that's a good point. I've already switched to extensions but still parent class is required. I will analyze it and try to do some PoC's within #1551

[MarcinVaadin]

Done, will be available in 9.0