Moves MockKExtension's unmockkAll behavior to the afterAll callback

[gmazzo]

This change is motivated by the comment I've dropped at #142 (comment).

MockKExtension is calling unmockkAll by default at the end of each test, which interferes with the @TestInstance(TestInstance.Lifecycle.PER_CLASS) configuration.

We discovered this issue after enabling junit.extensions.autodetection.enabled=true (by other rules, not this one) and all tests with cached mocks (per instance) started to fail because of the reset.

This PR moves the unmockkAll behavior to the afterAll callback, and also introduces a new @KeepMocks (and a mockk.junit.extension.keepmocks property) to allow disabling just this feature while keeping the others of MockKExtension.

[Raibaz]

This looks ok to me, thanks a lot for sending this through!

Could you also add a paragraph about unmocking and @KeepMocks in the user guide, in the "Junit5" section?

[gmazzo]

This looks ok to me, thanks a lot for sending this through!

Could you also add a paragraph about unmocking and @KeepMocks in the user guide, in the "Junit5" section?

Done!

[Raibaz]

Thanks a lot!

Not merging this right away as I want to make a release as soon as it's merged, otherwise the docs and the actual behavior of the library would not be the same.

Going to merge this ASAP though, probably some time next week.

[gmazzo]

Ready to merge then? I don't have merge rights

[gmazzo]

Thanks a lot!

Not merging this right away as I want to make a release as soon as it's merged, otherwise the docs and the actual behavior of the library would not be the same.

Going to merge this ASAP though, probably some time next week.

I'm very sorry, I didn't want to rush you into this with my "Ready to merge then? I don't have merge rights". I've commented while reviewing my "pendings" without refreshing the ticket first 🤦

[Raibaz]

No worries, I was ready to release anyway :)