vitest-dev/vitest · error · Error

Cannot create a benchmark project because the name

Error message

Cannot create a benchmark project because the name "${name}" is already in use.

What it means

For each benchmark-enabled project, Vitest synthesizes a sibling benchmark project auto-named `${projectConfig.name} (bench)`, or just `bench` when the project has no name. Both names go into the shared `names` set; if the generated benchmark name already exists, resolution aborts to prevent two projects shadowing each other in reports.

Solutions

Give every benchmark-enabled project a unique `name`.
Avoid naming a non-benchmark project with a string ending in ` (bench)` that another project would generate.
Disable `benchmark` on projects that should not spawn a benchmark variant.

Example fix

// before: two unnamed projects, both benchmark-enabled
projects: [
  { test: { benchmark: { include: ['bench/a.bench.ts'] } } },
  { test: { benchmark: { include: ['bench/b.bench.ts'] } } },
]

// after
projects: [
  { test: { name: 'a', benchmark: { include: ['bench/a.bench.ts'] } } },
  { test: { name: 'b', benchmark: { include: ['bench/b.bench.ts'] } } },
]

Defensive patterns

Strategy: validation

Validate before calling

// Ensure benchmark-suffixed names won't collide.
function assertBenchmarkNamesUnique(projects: Array<{ name?: string; benchmark?: { enabled?: boolean } }>) {
  const names = new Set(projects.map(p => p.name).filter(Boolean) as string[])
  for (const p of projects) {
    if (p.benchmark?.enabled === false) continue
    const benchName = p.name ? `${p.name} (bench)` : 'bench'
    if (names.has(benchName)) {
      throw new Error(`Benchmark project name '${benchName}' would collide. Give benchmark-enabled projects unique names.`)
    }
    names.add(benchName)
  }
}

Prevention

Name every benchmark-enabled project explicitly.
Avoid the literal suffix ` (bench)` in hand-authored project names.

When it happens

Trigger: `names.has(name)` true inside `expandBenchmarksInEntries`, where `name` is computed at resolveProjects.ts:993. Triggers when two projects produce the same suffix (e.g. two unnamed projects both yield `bench`), or a real project is already named exactly `'<x> (bench)'`.

Common situations: Multiple unnamed benchmark-enabled projects in one config; a project literally named `bench` while another unnamed benchmark project exists.

Related errors

AI-assisted analysis of vitest-dev/vitest@1fa9837ec2 (2026-08-11). Data as JSON: /api/errors/e5acc0bfb140fd6d. Report an issue: GitHub.

Appendix: source

Thrown at packages/vitest/src/node/projects/resolveProjects.ts:996

 */
function expandBenchmarksInEntries(
  entries: ResolvedProjectEntry[],
  names: Set<string>,
  benchmarkOnly: boolean,
): ResolvedProjectEntry[] {
  let lastGroupOrder = Math.max(0, ...entries.map(e => e.projectConfig.sequence.groupOrder))
  const result = [...entries]

  for (const entry of entries) {
    const benchmark = entry.projectConfig.benchmark
    if ((!benchmark.enabled && !benchmarkOnly) || entry.hidden) {
      continue
    }

    const name = entry.projectConfig.name ? `${entry.projectConfig.name} (bench)` : 'bench'

    if (names.has(name)) {
      throw new Error(`Cannot create a benchmark project because the name "${name}" is already in use.`)
    }
    names.add(name)

    const benchmarkConfig: ResolvedConfig = {
      ...entry.projectConfig,
      name,
      include: benchmark.include,
      exclude: benchmark.exclude,
      includeSource: benchmark.includeSource,
      coverage: {
        ...entry.projectConfig.coverage,
        enabled: false,
      },
      maxWorkers: 1,
      maxConcurrency: 1,
      testTimeout: entry.projectConfig.testTimeout < 60_000 ? 60_000 : entry.projectConfig.testTimeout,
      hookTimeout: entry.projectConfig.hookTimeout < 120_000 ? 120_000 : entry.projectConfig.hookTimeout,
      // `enabled` because the original entry might not be benchmark-enabled (when

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