Mocha test runner doesn't clear test filter

[nicojs]

Summary

The @stryker-mutator/mocha-runner test runner plugin doesn't clear the test filter after a run with a test filter. The consequence is an incorrect result. This can be seen in the report of Stryker itself in a number of places. For example:

https://dashboard.stryker-mutator.io/reports/github.com/stryker-mutator/stryker/master#core/initializer/presets/ReactPreset.ts

This file should be almost entirely green, since it is well tested 😇. However, you can see it isn't a.t.m. 👿

Current workaround: Don't use coverage analysis 'perTest' in conjunction with the mocha test runner.

Stryker config

module.exports = function(config){
  config.set({
    testRunner: 'mocha',
    coverageAnalysis: 'perTest'
  });
}

I'll be working on a fix.

[simondel]

Oh no...

[nicojs]

This simple test reproduces the problem:

it('should be able to clear the filter after a filtered run', async () => {
    const testHooks = wrapInClosure(testFramework.filter([test0, test3]));
    await sut.proxy.run({ testHooks });
    const actualResult = await sut.proxy.run({ testHooks: undefined });
    expect(actualResult.tests).lengthOf(5);
});

F.y.i. @MrFix93 this is the bug we've spotted together.