vitest-dev/vitest · error · Error

The browser configuration must have a "name" property. This…

Error message

The browser configuration must have a "name" property. This is a bug in Vitest. Please, open a new issue with reproduction

What it means

An internal invariant: after confirming instance.browser exists, Vitest reads instance.name. The name is assigned by Vitest during config normalization, so a missing/null name means normalization did not run correctly. The message explicitly says this is a bug in Vitest.

Solutions

Reinstall and rebuild Vitest to rule out a stale build.
Ensure a single Vitest version across the workspace.
Avoid manually constructing browser instance objects; declare them via config only.
If reproducible with standard config, file a Vitest issue with the reproduction.

Defensive patterns

Strategy: try-catch

Type guard

const instanceHasName = (inst: unknown): inst is { name: string; browser: string } =>
  typeof inst === 'object' && inst !== null && typeof (inst as any).name === 'string' && typeof (inst as any).browser === 'string'

Try / catch

try {
  await resolveProjects(...)
} catch (err) {
  if (err instanceof Error && err.message.includes('"name" property. This is a bug in Vitest')) {
  // rebuild/reinstall Vitest; report if reproducible
  throw new Error('Vitest failed to normalize browser instance names; rebuild and retry', { cause: err })
  }
  throw err
}

Prevention

Always declare instances via config (let Vitest normalize names).
Keep a single Vitest version; rebuild after source edits.
Do not hand-construct raw instance objects.

When it happens

Trigger: instance.name is null/undefined during instance expansion, which should not happen because Vitest derives names earlier in the pipeline.

Common situations: A broken/partial Vitest build, version skew between config normalization and resolution code, or a custom code path that constructs raw browser instance objects bypassing normalization.

Related errors

AI-assisted analysis of vitest-dev/vitest@1fa9837ec2 (2026-08-11). Data as JSON: /api/errors/1fc15837fd92680d. Report an issue: GitHub.

Appendix: source

Thrown at packages/vitest/src/node/projects/resolveProjects.ts:882

    }

    // Keep the parent in the entry list as `hidden` so a `TestProject` is
    // created (instances link to it via `_parent` for the browser provider).
    // The parent's name is removed from `names` because the instance names
    // take its place in the user-facing project list.
    names.delete(parentName)
    result.push({ ...entry, hidden: true })

    filteredInstances.forEach((instance, index) => {
      const browser = instance.browser
      if (!browser) {
        const nth = index + 1
        const ending = nth === 2 ? 'nd' : nth === 3 ? 'rd' : 'th'
        throw new Error(`The browser configuration must have a "browser" property. The ${nth}${ending} item in "browser.instances" doesn't have it. Make sure your${projectConfig.name ? ` "${projectConfig.name}"` : ''} configuration is correct.`)
      }
      const name = instance.name
      if (name == null) {
        throw new Error(`The browser configuration must have a "name" property. This is a bug in Vitest. Please, open a new issue with reproduction`)
      }
      if (instance.provider?.name != null && projectConfig.browser.provider?.name != null && instance.provider?.name !== projectConfig.browser.provider?.name) {
        throw new Error(`The instance cannot have a different provider from its parent. The "${name}" instance specifies "${instance.provider?.name}" provider, but its parent has a "${projectConfig.browser.provider?.name}" provider.`)
      }

      const provider = instance.provider?.name ?? projectConfig.browser.provider?.name ?? 'preview'

      // Browser-mode CDP only features:
      if (provider === 'preview' || !isChromiumName(provider, browser)) {
        const browserConfig = `
{
  browser: {
    provider: ${provider}(),
    instances: [
      ${(filteredInstances || []).map(i => `{ browser: '${i.browser}' }`).join(',\n      ')}
    ],
  },
}

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