vitest-dev/vitest · error · Error

`bench.from()` could not find a result file at

Error message

`bench.from()` could not find a result file at "${resolved}". Run the source benchmark first to create it.

What it means

`bench.from(name, source)` loads a previously stored benchmark baseline. When `source` is a string path, Vitest resolves it (with `${projectName}` substitution) and asks the server via `rpc().readBenchmarkResult(resolved)` for stored data. If nothing was written at that path, this error fires. Baselines are created by registering a benchmark with the `writeResult` option, which calls `writeBenchmarkResult` after a successful run.

Solutions

Run the source benchmark first — register it with `bench('src', { writeResult: './results/src.json' }, fn)` and ensure it runs (`bench('src', fn).run()` or via `bench.compare`).
Make the `writeResult` template in the source and the `source` argument to `bench.from()` use the identical path string and the same `${projectName}` substitution.
If using a function source instead of a string, return the `BaselineData` directly to bypass file lookup.
Verify the benchmark project's `projectName` config is identical between the writing run and the reading run.

Example fix

// before
bench('v1', { writeResult: './bench-v1.json' }, v1fn)
const baseline = bench.from('v1', './results/bench-v1.json') // wrong path

// after
bench('v1', { writeResult: './results/bench-v1.json' }, v1fn)
const baseline = bench.from('v1', './results/bench-v1.json')

Defensive patterns

Strategy: validation

Validate before calling

const exists = await rpc().readBenchmarkResult(resolved); if (exists == null) throw new Error(`run the source benchmark with writeResult='${resolved}' first`)

Type guard

null

Try / catch

try { reg = bench.from('base', './r.json') } catch (e) { if (/could not find a result file/.test(e.message)) { await writeSourceFirst(); reg = bench.from('base', './r.json') } else throw e }

Prevention

Keep the `writeResult` template and the `bench.from` source string in a shared constant.
Run the writing benchmark in the same Vitest invocation (or a prior CI step) before the reader.
Use the same `projectName` for both writer and reader to keep `${projectName}` substitution consistent.

When it happens

Trigger: Calling `bench.from('baseline', './results/my-bench.json')` before any benchmark has written results to that path. Also triggered by a mismatched `${projectName}` substitution — `source` uses `./${projectName}/baseline.json` but the writer used a different project name, so the resolved paths diverge.

Common situations: Running `bench.from` in CI before the source benchmark ran in the same or a prior step; the `writeResult` template in the source benchmark does not match the `from` source string; the results directory was cleaned; the project name changed between write and read.

Related errors

AI-assisted analysis of vitest-dev/vitest@1fa9837ec2 (2026-08-11). Data as JSON: /api/errors/56a67719177d166c. Report an issue: GitHub.

Appendix: source

Thrown at packages/vitest/src/runtime/benchmark.ts:244

}

export function createBench(
  test: Test,
  config: SerializedConfig,
  moduleRunner: TestModuleRunner,
): Bench {
  const pending = new Set<BenchRegistration<any>>()

  const resolveTemplate = (template: string) => substitutePath(template, config.benchmark.projectName)

  const resolveFromSource = async (source: string | BenchFromSource): Promise<BaselineData> => {
    if (typeof source === 'function') {
      return source()
    }
    const resolved = resolveTemplate(source)
    const data = await rpc().readBenchmarkResult(resolved)
    if (data == null) {
      throw new Error(`\`bench.from()\` could not find a result file at "${resolved}". Run the source benchmark first to create it.`)
    }
    return data
  }

  const taskFromBaseline = (
    name: string,
    data: BaselineData,
  ): TestBenchmarkTask => ({
    name,
    latency: data.latency,
    throughput: data.throughput,
    period: data.period,
    totalTime: data.totalTime,
    rank: 0,
    fromStore: true,
  })

  const createCompareStorage = <T extends string>(

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