babel-jest module isn't found if not added directly

[IlCallo]

Hi guys, I noticed today that I cannot run tests anymore if I have setup Babel transpilation for JS files.

I get this error

● Validation Error:

  Module babel-jest in the transform option was not found.
         <rootDir> is: D:\Sources\smile80\libs\renderer

  Configuration Documentation:
  https://jestjs.io/docs/configuration.html

I checked my yarn.lock file and babel-jest is actually present in the file, but there's no folder into node_modules, that may be the cause.
Lately I upgraded to yarn 1.16.0, so I tried downgrading to 1.15.2, but with no results: same error.

If I add it as a direct dependency, it restarts working.
I'm pretty confused right now, I checked my history and I'm pretty sure that 2 days ago I launched my tests without problems and without babel-jest as direct dependency.

[wtho]

The reason might be that some/several other packages had babel-jest as a dependency and something about that changed. Sometimes, if possible, packages get deduped by npm/yarn to save space and are therefore put in the root of node_modules only once, if several other package use a compatible common version.

If this is not the case, each package might have its inner node_modules folder with the respective version of the dependency.

As npm heavily relies on semantic versioning, even running npm on the same day can/will result in different packages (if some package somewhere in the dependency tree changed just a minor version) and deduped packages might not be in the root anymore, as they were yesterday.

A general rule of thumb is: if a package is imported/required directly by your project, it should be declared in package.json.

[IlCallo]

Make sense, even if it should be a rare occurring: all my dependencies are version-locked.

That said, maybe it should be added, in the section I linky l linked, that you have to install babel-jest as direct dev-dependency

[thymikee]

If babel is used in any way, babel-jest is required by Jest to be in your dev dependencies. It's in the docs on Babel integration. Feel free to add a note

[wtho]

all my dependencies are version-locked

Just to avoid confusion, version-locking in npm can only be achieved by installing packages only using npm ci after package-lock.json, which will install the exact versions described in package-lock.json.

Anyway, I will close this issue for now, feel free to reopen in case you feel this is unresolved.

[IlCallo]

I use yarn, I think that behaviour is the default.

I'll PR a note on the readme as soon as I have some time to add the note

[wtho]

Oh yeah, yarn is locked to yarn.lock as long as the dependencies in package.json do not change.

[IlCallo]

If babel is used in any way, babel-jest is required by Jest to be in your dev dependencies. It's in the docs on Babel integration. Feel free to add a note

I guess you meant the first line of this page.
I'll open a PR adding the link to that page

[inlightmedia]

I ran into this when using yarn workspaces. One of my packages was using babel-jest for testing but when I added babel-jest to the package.json it would add to the repo's root yarn.lock file and not to the node_modules folder of the package. In my jest transform I was referencing babel-jest like this:

transform: {
        "^.+\\.(js|jsx|ts|tsx)$": "./node_modules/.bin/babel-jest",
},

To fix, I just removed the relative path:

transform: {
        "^.+\\.(js|jsx|ts|tsx)$": "babel-jest",
},

[aManNamedJed]

@inlightmedia Not all heroes wear capes, or perhaps you do, in which case I like you even more. Thank you!