[Bug]: Use .mts file extension with ts-jest

[michaelwittwer]

Version

28.0.7

Steps to reproduce

Steps:

1. clone my repo at https://github.com/shiftcode/ts-jest-issue
2. npm install
3. npm run test

Expected behavior

Test should run successfully without any complains.

Actual behavior

I am seeing the following WARN message from ts-jest:

ts-jest[ts-jest-transformer] (WARN) Got a unknown file type to compile (file: /Users/michaelwittwer/dev/shiftcode/esm-ts-jest/src/util.spec.mts). To fix this, in your Jest config change the transform key which value is ts-jest so that it does not match this kind of files anymore.

Which prevents the tsc compiler to compile the source to mjs.

Debug log

to long to be pasted here, you can execute npm run test:debug to see the log after checking out the repo

Additional context

No response

Environment

System:
    OS: macOS 12.4
    CPU: (10) arm64 Apple M1 Max
Binaries:
    Node: 16.13.2 - ~/.nvm/versions/node/v16.13.2/bin/node
    Yarn: 1.22.19 - /opt/homebrew/bin/yarn
    npm: 8.1.2 - ~/.nvm/versions/node/v16.13.2/bin/npm
npmPackages:
    jest: ^28.1.3 => 28.1.3

[michaelwittwer]

Thanks @ahnpnl. Any rough estimation, when this is released?

[ahnpnl]

Note that there is one issue is Jest resolver doesn't know how to resolve .mts file. You would run into some kinds of errors like

Cannot find module <a> from <b/a>

You would need to solve this by yourself by providing moduleNameMapper or a custom Jest resolver. It is out of scope for ts-jest

[michaelwittwer]

I don't fully get what you are saying. With ts-jest supporting .mts the source will be compiled to js using .mjs extensions, which then is treated as ESM by jest, right?

[ahnpnl]

In theory it should work that way and you have to run under ESM mode. Probably my playground ran into the problem with resolver, but just a note.

[anthonyhastings]

I also have a use case similar to @michaelwittwer where I'd like to have my test file extensions as .mts and also import .mjs files within them. I'm curious to know when this fix is going to be released, and if it fixes the aforementioned test repo. I tried making the fix changes directly in the local node modules folder but it didn't help matters. That might be due to the moduleNameMapper hinted at earlier in the thread but I'm not sure I fully understood that.

[ahnpnl]

Included in the new release, please also check doc https://kulshekhar.github.io/ts-jest/docs/guides/esm-support#support-mts-extension