Running Jest with --findRelatedTests

[RobertBroersma]

When running Stryker with Jest, it runs your entire test suite for every mutation. If you have a large test suite this can take quite some time.

Jest has an awesome flag called --findRelatedTests, which finds tests related to the file you pass as an arguments. E.g. jest --findRelatedTests index.js would only run the tests related to index.js. (Often used with lint-staged.

If it would be possible to pass the current mutation to the Test Runner, this would save a ton of time!

[simondel]

@nicojs What are your thoughts on this compared to doing code coverage analysis? To use this feature, we'll need to let the testrunner know which file contains a mutant.

[nicojs]

Hmm sounds like a fairly straightforward solution that could speed things up for jest users. We would have to make sure we add integration tests for it. Also: we might need to add it as a confirmation option, as it might result in unexpected behavior, right?

This is the documentation for the feature: https://jestjs.io/docs/en/cli#findrelatedtests-spaceseparatedlistofsourcefiles

@RobertBroersma thanks for reporting this. Do you want to take a shot at it?

[RobertBroersma]

@nicojs I suppose the option could be added to the config file, perhaps even supporting the --bail flag, which stops jest as soon as a test fails (mutant killed, why kill it again).

I would like to have a crack at it, but I'd need to see if I can get some company time allocated to this, otherwise do it in my spare time. If you could give me some pointers on where to start that would be great!

[RobertBroersma]

PR Opened #1235