Is it possible to collect test coverage with node:test and esm-loaders like tsimp?

[krutoo]

Node.js Version

v24.1.0

NPM Version

11.3.0

Operating System

Darwin MSK-G4LQ6YF03T.local 24.5.0 Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:29 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6030 arm64

Subsystem

Other

Description

Hi, in my small project I use native Node.js testing features and also tsimp to support TypeScript with type checking during compilation

I am also use setup script to apply happy-dom to my test environment

I am running my tests like this:

node --import tsimp/import --import ./scripts/setup-tests.ts --experimental-test-coverage --test ./src/**/*.test.{ts,tsx}

Apparently according to resulting coverage table the resulting lines after compilation are checked, not the source code lines

It is possible to correctly collect test coverage for source lines not for compiled lines?

Minimal Reproduction

No response

Output

No response

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[avivkeller]

Try running your command with --enable-source-maps

[dax-side]

Yes, but it's tricky. node:test supports coverage with --experimental-test-coverage, but custom ESM loaders like tsimp can interfere with instrumentation. Coverage tools rely on controlling module loading, and ESM loaders may bypass that. For reliable coverage, consider pre-compiling with TypeScript and running without a loader.

[avivkeller]

@krutoo I'm closing this, I believe my answer resolved this issue. If there are more concerns, they may be due to the third party loaders you mentioned.

Feel free to ping me if I'm mistaken.

[krutoo]

@avivkeller Yes, looks like it works with --enable-source-maps, thank you.

But now I have a slightly different question and perhaps you can help.

Now the coverage includes files that are tests, literally those files that are present in the test glob

Why coverage does not ignores test files?

[avivkeller]

No problem! I wrote https://nodejs.org/dist/latest/docs/api/cli.html#--test-coverage-exclude with that in mind.