Integrate coverage testing somehow

[abingham]

It would be nice to be able to constrain which tests get run based on coverage analysis. That is, when a change is made, determine what gets changed and only apply mutation to that section. Moreover, use coverage information to then only run the tests that apply to the mutated parts.

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• Bitbucket: https://bitbucket.org/austin_bingham/cosmic-ray/issue/20
• Originally reported by: austin_bingham
• Originally created at: 2015-03-26T15:58:16.593

[drorasaf]

In order to do so, don't we need to serialize the nodes between every run?

[abingham]

don't we need to serialize the nodes between every run?

I don't think so. We'll rely on a coverage tool to tell us the correspondence between tests and code-under-test. Then when there are changes we can determine which tests to run (ie those which correspond to changed lines) and which parts of the code to mutate (ie those which were changed).

This leaves a lot of unanswered questions, of course. Can coverage tools even give us this information? How will we need to rework the test runners (and maybe other parts of CR)? Do the underlying test systems allow us to be that selective about which tests are run? A lot of questions.

But now, I don't think we need to to anything as heavey-weight as serializing AST nodes. The approach I'm describing here heuristic; it's designed to be "pretty good" and provide easy performance gains.

[rob-smallshire]

I just had the same idea while I was waiting for Cosmic Ray to do its thing. It's sort-of obvious, so I'm not surprised it has already been suggested.

It seems to me this could provide a huge performance win.

[blueyed]

For pytest there is testmon, which might be useful to hook into.

There's an issue where the author of mutmut gave some insights of a slowdown when using it though (at tarpas/pytest-testmon#76).

[rob-smallshire]

There's an interesting thread here on extracting this information from coverage: https://bitbucket.org/ned/coveragepy/issues/170/show-who-tests-what

[abingham]

It seems to me this could provide a huge performance win.

In my thinking, this is one of the only ways to get mutation testing working in daily continuous integration processes on projects of any real size.

[rob-smallshire]

Bingo?! https://github.com/chrisbeaumont/smother