Support for analyzing diffs and only running mutation on the diffs

[SxMShaDoW]

Hi,

Is there a way to only run mutation testing on the diffs of files?

I am currently running mutation testing on all my PR builds, but as my service complexity expands, the longer mutation testing takes to run. When I use the "withHistory" it goes lightning fast locally, but that isn't possible since CI/PR builds spin up new instances and git clone the code down.

If there isn't a way to do so, I included a user story below. Let me know how I can help!

As a developer, I would like to run a fast set of mutation testing on all my pull request builds, so that I can increase confidence in tests from other contributors.

Requirements

• Be able to run mutation testing on a pull request build
• pitest is able to understand git diffs and run mutation testing on just the diff
• can utilize the github pull request build functionality and cloudsbee's one.

Examples of other frameworks doing this:

• Sonarqube. It analyzes the diff using a preview mode and only scans the changes in those files.

Current things that pitest supports:

• modifying changes locally and running scmMutation.
• running changes withHistory to speed up builds locally (doesn't work on PR / CI if people spin up a new instance every-time like (travis/circle/appvoyer)
• ability to analyze from last commit (don't really understand how this one works because the documentation isn't really flushed out, but didn't seem to help if this was on or off on the PR build)

[pedrorijo91]

been digging into this as well. for my PoC project, I'm using travis, and it seems it would be possible to use the withHistory flag to support this, since travis allows to keep cached directories between builds: https://docs.travis-ci.com/user/caching/#arbitrary-directories

Probably other CI's also have such feature. Have you looked at it?