Coverage issues

[SamuelWei]

Running the coverage gives me a strange output, missing some code blocks, even if the code should perform exactly the same

Missing coverage in lines 291-305

Working: Saving promise to an variable and using it for .then and .catch

Working: Saving promise to an used variable

Is there something working with the coverage or am I missing something obvious?

I have worked through many issues and recommendations including multiple jest and vue-jest versions.
I also used v8 and the default babel coverage reporter. However both coverage providers cause issues in my vue2 project and none is working really accurate.

My current config:
vue: 2.6.14
@vue/vue2-jest: 29.1.1
jest: 29.2.1

jest.config.js

....
transform: {
    '^.+\\.vue$': '@vue/vue2-jest',
    '^.+\\.js$': 'babel-jest'
},
....

[SamuelWei]

I traced the issue down to jests pre-processor https://github.com/facebook/jest/blob/6e5b1d60a1214e792b5229993b5475445e9c1a6e/e2e/coverage-transform-instrumented/preprocessor.js#L24

I traced the issue down to babel-jest
https://github.com/facebook/jest/blob/6e5b1d60a1214e792b5229993b5475445e9c1a6e/packages/babel-jest/src/index.ts#L52

If the coverage is set to babel it is adding the /* istanbul ignore next */ to many lines which are therefore ignored in the coverage. Using v8 doen't add this line or /* c8 ignore next */.

In the vue-jest process function a config is passed to babel-jest having the variable instrument true for babel and false for v8

vue-jest/packages/vue2-jest/lib/process.js

Line 49 in dbe8022

const result = transformer.process(scriptPart.content, filePath, config)

I don't know why this is done and where to change this config value.

@lmiller1990 Do you know why this is happening?
@SimenB Do you know why this istanbul ignore next was added to the preprocessor ?

[lmiller1990]

In the vue-jest process function a config is passed to babel-jest having the variable instrument true for babel and false for v8

I am not sure why this would be happening. If you play around in node_modules/vue-jest, are you able to get something working? Happy to accept a PR - I'm not working on Vue Jest (other than critical bug fixes/security issues) nowadays. I'm don't expect to be able to spend much time debugging this.

Do you think there's an issue in Jest or this bug is localize to Vue Jest?

[SamuelWei]

I just had a deeper look and found the instrument = true comes from https://github.com/facebook/jest/blob/6e5b1d60a1214e792b5229993b5475445e9c1a6e/packages/jest-transform/src/ScriptTransformer.ts#L703

[SimenB]

@SimenB Do you know why this istanbul ignore next was added to the preprocessor ?

Not sure - it was added back in jestjs/jest#785 before my involvement with the project. However, the issue that PR talks about (babel's helpers) should have been solved by supporting source maps, which we've done for a few years at this point. Happy to take a PR removing it if it doesn't do anything useful anymore 🙂