[Bug]: Jest incorrectly writes new snapshots in CI

[billyjanitsch]

Version

27.4.7

Steps to reproduce

1. Clone https://github.com/billyjanitsch/jest-ci-snapshot-bug
2. Run npx jest --ci. Note that the test fails, refusing to write the new snapshot.
3. Run CI=1 npx jest. Note that the test passes, and the snapshot is written. Also note that terminal colors are disabled (CI mode).
4. Run npx jest. Note that terminal colors are enabled (not CI mode).

Expected behavior

Step 3 should behave the same as step 2: Jest should refuse to write the snapshot and the test should fail.

Actual behavior

In step 3, the snapshot is written and the test passes.

Additional context

The issue was introduced in #9924 (as noted in #9924 (comment)), so it has been present since Jest 27.0.0. The problem is here:

https://github.com/facebook/jest/blob/161452447a8cbc071447ba92a03efc63da1dd0b7/packages/jest-config/src/normalize.ts#L1123-L1128

jest-config pulls the default value directly from argv.ci when deciding on the value of updateSnapshot.

Note that the problem isn't that Jest is failing to pick up on the CI env variable at all, because the difference between steps 3 and 4 shows that Jest is recognizing the presence of the variable and altering its behavior accordingly. It's specific to snapshot updating.

Environment

System:
    OS: macOS 10.15.7
    CPU: (16) x64 Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
  Binaries:
    Node: 16.13.0 - ~/.local/share/nvm/v16.13.0/bin/node
    Yarn: 1.22.11 - /usr/local/bin/yarn
    npm: 8.3.0 - /usr/local/bin/npm
  npmPackages:
    jest: ^27.4.7 => 27.4.7

[cola119]

I'm working on this.

[SimenB]

https://github.com/facebook/jest/releases/tag/v28.0.0-alpha.1

[github-actions]

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