Allow custom coverage reporters

🚀 Feature Proposal

Allow jest to use custom coverageReporters.

Motivation

Only istanbuljs coverage reporters can be used so far. But istanbuljs has limited number of reporters which can’t cover all possible options.

E.g. I’ve needed a coverage reports to be in junit-xml format which isn’t present in istanbuljs library.

Example

It could be used just like test reporters.

// jest.config.js
{
  collectCoverage: true,
  coverageReporters: [require.resolve('<path to appropriate node_module>')],
  ...
}
//
{
  collectCoverage: true,
  coverageReporters: [
    'json',
    'text',
    [
      require.resolve('<path to appropriate node_module>'), { option: {}, ... }
    ] // with options
  ],
  ...
}

Workaround

Define custom test (not coverage) reporter. Implement onRunComplete method and extract coverage results from aggregatedResult.

class CustomCoverageReporter {
  ...
  onRunComplete(context: jest.Context, aggregatedResult: jest.AggregatedResult): void {
    // extract coverage here
  }
}

module.exports = CustomCoverageReporter;

// jest.config.js
{
  ...
  collectCoverage: true,
  reporters: [require.resolve('<path to CustomCoverageReporter>')]
}

But you need be aware that it’ll be invoked even if collectCoverage flag is set to false. So additional validations are required.

Pitch

Why does this feature belong in the Jest core platform?

It would be great to be able to export coverage reports in different desirable formats. This enhancement would provide more flexibility.

[valoricDe]

I think it changed again and I haven’t worked on this a while. I guess this project does not help to understand internals or? https://github.com/dkelosky/jest-stare/blob/master/src/reporter/Reporter.ts

[YozhEzhi]

I think this one can be closed. Istanbul changed the way they integrate the reporter. You just need to export a class with a function execute(results) and then you receive the coverageMap

Hi! Could you please share link for example about how to receive the coverageMap?

I solved my case like this, but I think this is bad idea:

import libCoverage from 'istanbul-lib-coverage';
import { CoverageReporter } from '@jest/reporters';

class Reporter extends CoverageReporter {
    async onRunComplete(): Promise<void> {
        // @ts-ignore
        const { map } = await super._getCoverageResult();
        if (!map) return;

        const coverageMap = libCoverage.createCoverageMap(map);
       // ...
       }
}