[proposal] Fixture/snapshot tests - write in separate files

🚀 Feature Proposal

Allow each fixture/snapshot test to be written to separate file WITHOUT wrapping snapshot output into exports property.

Motivation

It would be highly useful for projects like babel to treat their current fixture tests (actual.js / expected.js pairs) as Jest snapshots. This would allow integrating with jest more easily and using snapshot features for those tests (like -u)

Example

API would have to be decided, this is just a one proposal:

expect('test/fixtures/**/actual.js', ({ filename, code }) =>
  babel.transform(code, { 
    filename
  }).code
).toMatchFixtureSnapshot('expected.js')

Pitch

This with inline snapshot features would make a nice, complete package and cover most use cases.

[Andarist]

I don’t get why this new matcher would improve on the current approach

The problem with current approach is that snapshots are colocated to the file that is doing an expect call. With fixtures such as in babel desired scenario is to keep expected snapshots colocated with input fixtures.

Is the exports causing issues?

Taking babel as an example. Keeping expected.js without exports wrapper is way nicer, because the output is actual code and when inspecting such an output file you get i.e. syntax highlighting for free.

[SimenB]

We should stick links to https://github.com/americanexpress/jest-image-snapshot and https://github.com/satya164/jest-file-snapshot in https://jestjs.io/docs/snapshot-testing.

PR is still welcome to make _updateSnapshot public - probably under a more descriptive name?