🐛 BUG: Vitest code coverage does not work when using `@cloudflare/vitest-pool-workers`

[NuroDev]

Which Cloudflare product(s) does this pertain to?

Workers Vitest Integration

What version(s) of the tool(s) are you using?

0.1.2

What version of Node are you using?

20.5.1

What operating system and version are you using?

macOS Sonoma 14.1.1

Describe the Bug

Observed behavior

Following the basic example from your announcement blog post I created a basic project with it & attempted to enable code coverage by adding the @vitest/coverage-v8 package & added coverage: { enabled: true } property to my Vitest config.

Expected behavior

When running Vitest you get the following error:

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Unhandled Errors ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Vitest caught 1 unhandled error during the test run.
This might cause false positive tests. Resolve unhandled errors to make sure your tests are not affected.

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Unhandled Error ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
Error: No such module "node:inspector".
  imported from "Users/nuro/Desktop/vitest-test/node_modules/.pnpm/@[email protected][email protected]/node_modules/@vitest/coverage-v8/dist/index.js"
⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Steps to reproduce

• Follow the announcement post to set up a basic Vitest project

      1 .
      2 ├── src
      3 │   └── index.ts
      4 ├── tests
      5 │   └── basic.test.ts
      6 ├── package.json
      7 ├── pnpm-lock.yaml
      8 ├── tsconfig.json
      9 └── vitest.config.ts

• Add the @vitest/coverage-v8 package
• Add the following to the test object to enable code coverage

    coverage: {
      enabled: true,
    },

Please provide a link to a minimal reproduction

No response

Please provide any relevant error logs

No response

[mrbbot]

Hey! 👋 Thanks for raising this. Native code coverage via @vitest/coverage-v8 is not supported. You must use instrumented code coverage via @vitest/coverage-istanbul instead. Refer to the Vitest Coverage documentation for setup instructions. We've got a PR open to add this to the docs (https://github.com/cloudflare/cloudflare-docs/pull/13465), whilst we work on adding support for native coverage.

[mrbbot]

Support for native code coverage is tracked by internal ticket DEVX-1137 👍

[mrbbot]

For whoever ends up implementing this, I think this should be possible by starting an inspector server with Miniflare's inspectorPort option, then polyfilling the node:inspector module to report this URL for the started inspector URL. Something similar would be required for https://github.com/cloudflare/workers-sdk/issues/5391. There's a patch in the DevProd team drive Brendan-handover folder that might be helpful.

[xxcheckmatexx]

Getting error via istanbul as well, for the starter hello world template.

TypeError: this.toSlices is not a function or its return value is not iterable
 ❯ IstanbulCoverageProvider.reportCoverage ../../node_modules/@vitest/coverage-istanbul/dist/provider.js:214:34
 ❯ Vitest.reportCoverage ../../node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:6537:7
 ❯ async file:/Users/ashrith/Development/react/feedback-circuit/feedback-circuit/node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:6328:7
 ❯ Vitest.runFiles ../../node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:6332:12
 ❯ Vitest.start ../../node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:6223:7
 ❯ startVitest ../../node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:13380:5
 ❯ start ../../node_modules/vitest/dist/cli.js:1386:17
 ❯ CAC.run ../../node_modules/vitest/dist/cli.js:13

Here is my vitest.config.ts

import { defineWorkersConfig } from '@cloudflare/vitest-pool-workers/config';

export default defineWorkersConfig({
  test: {
    globalSetup: ["./setup.ts"],
    coverage: {
      enabled: true,
      provider: 'istanbul',
      reporter: ['text', 'json', 'html'],
    },
    poolOptions: {
      workers: {
        wrangler: { configPath: './wrangler.toml' },
      },
    },
  },
});

Anyone tried the istanbul and has a workaround? Please help

[xxcheckmatexx]

Getting error via istanbul as well, for the starter hello world template.

TypeError: this.toSlices is not a function or its return value is not iterable
 ❯ IstanbulCoverageProvider.reportCoverage ../../node_modules/@vitest/coverage-istanbul/dist/provider.js:214:34
 ❯ Vitest.reportCoverage ../../node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:6537:7
 ❯ async file:/Users/ashrith/Development/react/feedback-circuit/feedback-circuit/node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:6328:7
 ❯ Vitest.runFiles ../../node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:6332:12
 ❯ Vitest.start ../../node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:6223:7
 ❯ startVitest ../../node_modules/vitest/dist/vendor/cli-api.RIYLcWhB.js:13380:5
 ❯ start ../../node_modules/vitest/dist/cli.js:1386:17
 ❯ CAC.run ../../node_modules/vitest/dist/cli.js:13

Here is my vitest.config.ts

import { defineWorkersConfig } from '@cloudflare/vitest-pool-workers/config';

export default defineWorkersConfig({
  test: {
    globalSetup: ["./setup.ts"],
    coverage: {
      enabled: true,
      provider: 'istanbul',
      reporter: ['text', 'json', 'html'],
    },
    poolOptions: {
      workers: {
        wrangler: { configPath: './wrangler.toml' },
      },
    },
  },
});

Anyone tried the istanbul and has a workaround? Please help

Issue is with vitest 1.4.0, anyone encountering this please use 1.3.0 hopefully they would have fixed it by then.

[stephensauceda]

I'm not even able to install @vitest/coverage-istanbul. The instructions (and the comment here) just refer to the vitest docs but trying to do npm install -D @vitest/coverage-instanbul fails due to unable to resolve dependency tree errors about peer dependencies. I've tried installing an older version of the instanbul package but none of them seem to work.

@cloudflare/vitest-pool-workers: 0.4.14 node v20.8.1

Just created the worker a couple days ago with npm create cloudflare

[carlosds731]

I'm not even able to install @vitest/coverage-istanbul. The instructions (and the comment here) just refer to the vitest docs but trying to do npm install -D @vitest/coverage-instanbul fails due to unable to resolve dependency tree errors about peer dependencies. I've tried installing an older version of the instanbul package but none of them seem to work.

@cloudflare/vitest-pool-workers: 0.4.14 node v20.8.1

Just created the worker a couple days ago with npm create cloudflare

I got it working by directly specifying the version of @vitest/coverage-istanbul. With these versions of the dependencies, it works for me

"devDependencies": {
    "@cloudflare/vitest-pool-workers": "^0.4.22",
    "@cloudflare/workers-types": "^4.20240806.0",
    "typescript": "^5.5.4",
    "vitest": "1.5.0",
    "@vitest/coverage-istanbul": "1.5.0",
    "wrangler": "^3.71.0"
  }

[rachelslurs]

I got it working with newer versions:

	"devDependencies": {
		"@cloudflare/vite-plugin": "^1.8.0",
		"@cloudflare/vitest-pool-workers": "^0.8.49",
		"@cloudflare/workers-types": "^4.20250703.0",
		"@types/node": "^24.0.10",
		"@vitest/coverage-istanbul": "^3.2.4",
		"typescript": "^5.5.2",
		"vite": "^6.3.5",
		"vitest": "3.2.4",
		"wrangler": "^4.22.0"
	}

import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        wrangler: { configPath: "./wrangler.toml" },
      },
    },
    coverage: {
      reporter: ["text", "json-summary", "json"],
      reportOnFailure: true,
      provider: "istanbul",
    },
  },
});