vitest-dev/vitest · error · Error

Benchmark provider loaded from "${provider}" did not have a

Error message

Benchmark provider loaded from "${provider}" did not have a default export.

What it means

Thrown by `loadProviderModule` (benchmark.ts:114) when the custom benchmark provider module imports successfully but has no `default` export (`mod.default == null`). Vitest expects the provider object (implementing `BenchmarkProvider.run`) to be the default export; a named-only export or a side-effect module is rejected.

Source

Thrown at packages/vitest/src/runtime/benchmark.ts:114

let cachedProvider: Promise<BenchmarkProvider> | undefined

async function loadProviderModule(
  provider: string,
  moduleRunner: TestModuleRunner,
): Promise<BenchmarkProvider> {
  let mod: Record<string, any>
  try {
    mod = await moduleRunner.import(provider)
  }
  catch (error) {
    throw new Error(
      `Failed to load benchmark provider from "${provider}".`,
      { cause: error },
    )
  }
  if (mod.default == null) {
    throw new Error(
      `Benchmark provider loaded from "${provider}" did not have a default export.`,
    )
  }
  return mod.default
}

/**
 * Resolves the benchmark provider for the current worker, importing a custom
 * provider module on first use. The result is cached for the lifetime of the
 * worker so a custom provider is imported at most once.
 */
export function resolveBenchmarkProvider(
  config: SerializedConfig,
  moduleRunner: TestModuleRunner,
): Promise<BenchmarkProvider> {
  if (!cachedProvider) {
    const provider = config.benchmark.provider
    cachedProvider = !provider

View on GitHub (pinned to d568f8ce37)

Solutions

1. Add `export default { async run(group) { /* return BenchResult[] */ } }` to the provider module.
2. Confirm the configured path points to the file with the default export.
3. Ensure the default export implements `BenchmarkProvider` (`run(group): Promise<BenchResult[]>`).

Example fix

// before
export const myProvider = { async run(group) { /* ... */ } }
// after
export default { async run(group) { /* return BenchResult[] */ } }

const mod = await import(providerPath)
if (mod.default == null) throw new Error(`${providerPath} must have a default export`)

const hasDefaultProvider = (m: Record<string, unknown>): m is { default: { run(g: any): Promise<any[]> } } =>
  typeof m.default === 'object' && typeof (m.default as any)?.run === 'function'

When it happens

Trigger: Authoring a benchmark provider with `export const provider = { run(...) {} }` and no default export; a provider whose default export is conditionally undefined; pointing at a file that isn't the provider entry.

Common situations: Forgetting `export default` when writing a provider; refactoring that moved the implementation to a named export; loading the wrong module.

Related errors

• The vcsProvider module '${vcsProvider}' doesn't have a defau
• Failed to load benchmark provider from "${provider}".
• Custom CoverageProviderModule loaded from ${options.customPr
• Custom reporter loaded from ${path} was not the default expo
• benchmark provider did not return a result for "${name}"

AI-assisted analysis of vitest-dev/vitest@d568f8ce37 (2026-08-03). Data as JSON: /data/errors/199f83fe6a4695ab.json. Report an issue: GitHub.