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changedSince runs specs related to files with no diff

See original GitHub issue

🐛 Bug Report

Using the --changedSince flag, Jest will run specs related to files with no current code changes (no diff) but which were previously committed.

The description of this flag is: Runs tests related to the changes since the provided branch. I would expect changes in this context to mean code changes between the current and specified revision, not each individual commit.

To Reproduce

Steps to reproduce the behavior:

Check out a new branch from master
Commit a change to any file (example.js) which has a related spec (example.test.js). Adding a comment will do.
Remove the change to this file & commit again.
Check that there are no current changes with git diff origin/master. There should be none.
Run jest --changedSince origin/master
Output will show that example.test.js was run, even though example.js has no changes.

Expected behavior

example.test.js does not run

Link to repl or repo (highly encouraged)

https://github.com/finn-orsini/jest-changed-since-bug-poc

Run yarn
Check out branch changed_since_no_changes (See PR showing no code changes here)
Run yarn test

Output will show that sum.test.js was run:

$ jest --changedSince origin/master
 PASS  src/__tests__/sum.test.js
  ✓ adds 1 + 2 to equal 3 (4ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.119s

Note that running git log --name-only --pretty=format: HEAD ^origin/master (the command run by jest-changed-files) on this branch will include sum.js since a comment was added and removed in previous commits.

envinfo

  System:
    OS: macOS Mojave 10.14.6
    CPU: (8) x64 Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
  Binaries:
    Node: 8.16.2 - ~/.nvm/versions/node/v8.16.2/bin/node
    Yarn: 1.21.1 - ~/.nvm/versions/node/v8.16.2/bin/yarn
    npm: 6.4.1 - ~/.nvm/versions/node/v8.16.2/bin/npm
  npmPackages:
    jest: ^24.9.0 => 24.9.0