Incorrect Jest coverage

[stephane-arista]

When using @swc/jest to transpile ts to commonjs and running jest --coverage certain branches are shown as not covered (console logging in these branches show that tests do run the code path). Using babel to transpile and run the tests shows the correct coverage.

[pspeter3]

I added this to my Jest configuration in package.json which seemed to help.

"jest": {
    "collectCoverage": true,
    "transform": {
      "^.+\\.(t|j)sx?$": [
        "@swc/jest",
        {
          "sourceMaps": true
        }
      ]
    }
  }

[krutoo]

@pspeter3 Thank you for your code snippet, it helps, but now there is another problem:

It looks like not covered code highlights are not displayed correctly.

There is an example of coverage report from project with:

• jest@27.3.1
• @swc/core@1.2.118
• @swc/jest@0.2.11

the yellow highlight here says that the comma is supposedly not covered

[sebald]

@krutoo ran into the same issues and guessed it is caused by the conversion to older JS syntax. We could fix these false-positives by targeting a newer ES version.

  transform: {
    '^.+\\.(t|j)sx?$': [
      '@swc/jest',
      {
        jsc: {
          target: 'es2021',
        },
        sourceMaps: true,
      },
    ],
  },

[krutoo]

@sebald Thank you, looks like it realy works with target: "es2021"

[JoshuaKGoldberg]

Another reproduction here: typescript-eslint/tslint-to-eslint-config#1367

I ended up only needing target: "es2021". Thanks!

[kdy1]

I think swc reusing span for various places may cause this.

Can you try https://sokra.github.io/source-map-visualization/#custom by manually invoking swc?

[bobaaaaa]

@kdy1 does this help? Maybe the Object.keys(_node).forEach produces the mismatch? Jest complains that this line is not covered: export * as node from './BodyNodesBuilder';

Edit: tested with

• @swc/jest 0.2.20
• jest 27.5.1

[kdy1]

@bobaaaaa Can you share some code? I think the test file would be enough, as it does not have good sourcemap.

[kdy1]

Oh... Maybe assumption about monotonic increment of source map position can be the cause.
I'll add it to my tasklist

[bobaaaaa]

@kdy1 You can find it here: https://gist.github.com/bobaaaaa/3649b3a7e6312793a257bf67c500128a
Let me know if something is missing.

(thx for investigating ❤️)