[Bug]: --watch with coverage produces inconsistent reports

[zebreus]

Version

28.1.3

Steps to reproduce

0. Clone https://github.com/Zebreus/jest-watch-bug-repro
1. Dirty the file alpha.js ( echo " " >> alpha.js )
2. Run jest --watch --coverage --watchAll
3. Observe that coverage is reported for all files
4. Press o
5. Observe that coverage is only reported for changed files (only alpha.js)
6. Press a
7. Expect a coverage report for all files.
8. Observe that coverage is still only reported for changed files.

This applies to all filters. Once you activate coverage reporting only for changed files, you can't switch back to coverage for all files without restarting jest.

Expected behavior

I have a few ideas about what could be expected, but I think it is quite hard to get this right.

A: Watch reports coverage for all files, unless it is testing only changed files.

If you specifically run a test regex the user is probably also interested in the coverage report for the unchanged files that were involved.

B: Watch reports only coverage for changed files.

This would make coverage reports useful when working on individual files.

C: Guess which files the user is interested in

Maybe figure out which files were involved in the executed tests and only print their coverage. We probably even can figure out which functions were involved and only report their coverage.

Actual behavior

Watch with coverage has no documentation afaik.

If you run jest --watch --coverage it only prints the coverage report for changed files, even if you interactivly specify a custom test regex.

If you run jest --watch --coverage -t something it prints the coverage report for all files.

Once jest starts printing the report only for changed files, there is no way back to printing it for all files.

Additional context

The behaviour of watching only changed files with coverage activated can be quite unexpected and confusing.

I think generating coverage reports without running all tests is a bad idea, because there will be files that only have some tests executed.

Related issues

• '--coverage --watch' should calculate coverage for all files at first iteration #8992 Multiple users expected a coverage report
• Coverage in Watch mode only for tested files #10272 Stale issue about generating coverage report only for relevant files
• Had Code Coverage Previously, but now Disappeared #9319 Coverage report for clean repo expected (CRA)
• [Bug]: collectCoverageFrom not working for react components #13095 Coverage report for clean repo expected (CRA)

Environment

System:
    OS: Linux 5.18 NixOS 22.05 (Quokka) 22.05 (Quokka)
    CPU: (16) x64 11th Gen Intel(R) Core(TM) i9-11950H @ 2.60GHz
  Binaries:
    Node: 16.16.0 - /nix/store/vs43ydaw3k0pqa2z3s9mprqaymmbj66p-nodejs-16.16.0/bin/node
    Yarn: 1.22.18 - /nix/store/8fa68i731y9pda2jh52caqc26cqi6h2d-yarn-1.22.18/bin/yarn
    npm: 8.11.0 - /nix/store/vs43ydaw3k0pqa2z3s9mprqaymmbj66p-nodejs-16.16.0/bin/npm
  npmPackages:
    jest: ^28.1.3 => 28.1.3

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