Snapshot serializers added with expect.addSnapshotSerializer are not used

[askoufis]

🐛 Bug Report

Custom snapshot serializers added with expect.addSnapshotSerializer are not used. Only custom snapshots serializers configured via snapshotSerializers actually work.

This behaviour appears to have broken in version 8.

To Reproduce

• git clone https://github.com/askoufis/jest-puppeteer-repro
• pnpm install
• pnpm test

The test in foo.test.js is run. This has a custom serializer added that prepends some text to the snapshot. However the snapshot does not contain this test, which is a bug.

• git switch jest-puppeteer-7
• pnpm install
• pnpm test

This branch has jest-puppeter@7 installed. The snapshot serializer works in this case.

• git switch config-snapshot-serializers
• pnpm install
• pnpm test

This branch has the snapshot serializer configured in the jest config instead of the test file, and it's using jest-puppeteer@8. The snapshot now fails as the serializer has prepended some text to the snapshot, which is the expected behaviour.

Expected behavior

Custom snapshot serializers added with expect.addSnapshotSerializer should work.

Link to repl or repo (highly encouraged)

https://github.com/askoufis/jest-puppeteer-repro

System info

Paste the results here:

## System:
 - OS: macOS 13.2.1
 - CPU: (10) arm64 Apple M1 Pro
 - Memory: 4.52 GB / 32.00 GB
 - Shell: 3.6.1 - /opt/homebrew/bin/fish
## Binaries:
 - Node: 16.20.0 - ~/.local/share/.volta/tools/image/node/16.20.0/bin/node
 - Yarn: 1.22.19 - ~/.local/share/.volta/tools/image/yarn/1.22.19/bin/yarn
 - npm: 8.19.4 - ~/.local/share/.volta/tools/image/node/16.20.0/bin/npm
 - Watchman: 2023.05.01.00 - /opt/homebrew/bin/watchman
## npmPackages:
 - jest-puppeteer: ^8.0.6 => 8.0.6

[gregberge]

Hello @askoufis, thanks. I think it is a problem in the overriding of expect.

[askoufis]

Did a bit of debugging. To me, the overriding of expect is correct. It's similar enough to the code in expect-puppeteer v7 (when this used to work) that I don't think it's the culprit.

What's interesting is that when calling addSnapshotSerializer, which is just an alias for addSerializer, the PLUGINS array is updated correctly. However, when getSerializers is called later on (internally within jest somewhere), the PLUGINS array is back to its original state with only 7 elements (you'd expect there to be at least 8).

[askoufis]

Thanks for the fix! :)