Use PhpUnit as test-runner

[allanpaiste]

Is your feature request related to a problem? Please describe.

Currently the test scenarios are based on custom scripts that do not allow convenient development flow and test runner utilization via IDE. It also introduces avoidable overhead for new developers who otherwise could tap into their previous experience with commonly used testing frameworks/runners.

Describe the solution you'd like

Port over the installations/scenarios/assertions to run with PhpUnit runner. Make sure that IDE picks up the tests properly.

Describe alternatives you've considered

Have not seen a real need to consider any alternatives here as PhpUnit is relatively light-weight and well known.

Additional context

This change would also make it easier to run the tests on different platforms as long as php is available. It will also make much easier for users to step through the patch applying flow.