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🐛 BUG: vitest-plugin coverage shim doesn't handle __vitest_stopV8Coverage under vitest 5 #16238
Description
What versions & operating system are you using?
System:
OS: macOS 27.0.1
CPU: (10) arm64 Apple M4
Binaries:
Node: 26.8.2
npm: 11.19.1
npmPackages:
@cloudflare/vitest-plugin: 1.4.0
@vitest/coverage-v8: 5.0.4
vitest: 5.0.4
wrangler: 4.149.0
Please provide a link to a minimal reproduction
Five small files, inline:
package.json
{
"type": "module",
"devDependencies": {
"@cloudflare/vitest-plugin": "1.4.0",
"@vitest/coverage-v8": "5.0.4",
"vitest": "5.0.4",
"wrangler": "^4.135.0"
}
}wrangler.jsonc
{ "name": "repro", "main": "src/index.ts", "compatibility_date": "2026-10-01", "compatibility_flags": ["nodejs_compat"] }src/index.ts
export default {
fetch() {
return new Response("ok");
},
};test/index.test.ts
import { SELF } from "cloudflare:test";
import { expect, it } from "vitest";
it("responds", async () => {
const res = await SELF.fetch("https://example.com");
expect(await res.text()).toBe("ok");
});vitest.config.ts (fsModuleCache is off only to avoid a separate vitest 5 bug; see #16237)
import { cloudflareTest } from "@cloudflare/vitest-plugin";
import { defineConfig } from "vitest/config";
export default defineConfig({
plugins: [cloudflareTest({ wrangler: { configPath: "./wrangler.jsonc" } })],
test: { fsModuleCache: false, coverage: { provider: "v8" } },
});Then npx vitest run --coverage.
Describe the Bug
Under vitest 5, @vitest/coverage-v8 drives coverage in the isolate through __vitest_browser_runner__.commands.triggerCommand. Its stopCoverage sends __vitest_stopV8Coverage at the end of every test file (unless isolate: false). The shim the plugin installs in the runner Durable Object handles __vitest_startV8Coverage, __vitest_takeV8Coverage and __vitest_writeCoverageFile. It has no branch for __vitest_stopV8Coverage, so the command reaches assert.strictEqual(command, "__vitest_writeCoverageFile") and throws. This is still the case on main in packages/vitest-plugin/src/worker/index.ts.
Expected: coverage runs cleanly and exits 0.
Actual: the test passes, but Vitest reports one unhandled error per test file and exits 1. The coverage report itself is unaffected: the numbers are identical with the fix below. The inspector session isn't closed at the end of the file; the next __vitest_startV8Coverage closes it.
Suggested fix (we're carrying it as a postinstall patch against 1.4.0's built output, and the error is gone):
if (command === "__vitest_stopV8Coverage") {
await this.stopV8CoverageSession();
return "";
}placed before the __vitest_writeCoverageFile assertion.
Please provide any relevant error logs
AssertionError: Values are not strictly equal:
- __vitest_stopV8Coverage
+ __vitest_writeCoverageFile
❯ assert.strictEqual node-internal:internal_assert:196:11
❯ Object.triggerCommand index.mjs:863:11
❯ triggerCommand node_modules/@vitest/coverage-v8/dist/browser.js:7:55
❯ Object.stopCoverage node_modules/@vitest/coverage-v8/dist/browser.js:24:9
❯ stopCoverageInsideWorker node_modules/vitest/dist/chunks/coverage.-bm5IxnW.js:22:58
Activity
workers-devprod commentedon Oct 13, 2026
Automated triage
Issue assessment
bug(high)package:vitest(high)Actionability and missing information
Under vitest 5, the vitest plugin's runner coverage shim lacks a __vitest_stopV8Coverage branch, so the writeCoverageFile assertion throws an unhandled error per test file and vitest exits 1; the report includes versions, minimal repro, expected and actual behavior, and error output.
Reproduction reason: The report describes a defect that plausibly persists in the current plugin and supplies a complete minimal reproduction: versions, config files, command, expected and actual behavior, and error output.
Reproduction
Evidence and attempted steps
Steps attempted:
pnpm install --no-frozen-lockfile # in /workspace/repro-work/project./node_modules/.bin/vitest run # exit=0, 1 test passed, no errors./node_modules/.bin/vitest run --coverage # exit=1, 'Vitest caught 1 unhandled error'grep -n '__vitest_stopV8Coverage|__vitest_writeCoverageFile' node_modules/vitest-plugin/dist/worker/index.mjsExpected behavior: Coverage runs cleanly and exits 0 (per the issue): vitest run --coverage completes with no unhandled errors, the test passes, and the v8 coverage report is produced.
Observed behavior: vitest run --coverage exits 1. The test passes (1/1) and the v8 coverage report is still emitted (index.ts 100%), but Vitest reports 'Vitest caught 1 unhandled error during the test run': AssertionError 'Values are not strictly equal: - __vitest_stopV8Coverage + __vitest_writeCoverageFile' thrown at Object.triggerCommand index.mjs:863:11 (the plugin's worker shim), reached via the coverage-v8 package's stopCoverage and vitest's stopCoverageInsideWorker; the stack frame matches the issue's log exactly. A baseline run without --coverage exits 0 with no errors.
Artifact: Download reproduction archive (Cloudflare Access required).
This summary was generated by an LLM and may contain errors. Please verify its findings.
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@workers-devprod reproduce: Attempt to reproduce the issue using its description and recent comments.dario-piotrowicz commentedon Oct 28, 2026
Thanks for the issue @colby-makowsky 🙏
I'm closing it since I believe that this has already been addressed by #16248
If you disagree please feel free to reopen this or create a new issue