Hello, in ParaTest we need to be able to run subsets of the Test Suite and then merge the results in a single output.
\PHPUnit\TestRunner\TestResult\TestResult does this job flawlessly, but it only covers the tests' output.

The current \PHPUnit\Runner\ResultCache\DefaultResultCache doesn't allow ParaTest to run different jobs each with its own cache file and then merge them all together.

I'm here to ask you to implement a way to do that.

Few questions you may answer:

1. Q: What does the merge functionality should do if the version differs between the two instances?
   A: Don't care, I'm fine to raise an Exception
2. Q: What does the merge functionality should do if multiple defects or times exist for the same $id?
   A: Don't care, it won't happen in ParaTest, I'm fine to raise an Exception