vitest-dev/vitest · error · TypeError

vitest.mergeReports() expects all paths in "${blobsDirectory

Error message

vitest.mergeReports() expects all paths in "${blobsDirectory}" to be files generated by the blob reporter, but "${filename}" is not a valid blob file

What it means

Thrown as a `TypeError` by `readBlobs` (blob.ts:135) when a file in the merge-reports directory parses via `flatted.parse` but the resulting tuple has no `version` field. A valid blob file is a flatted-stringified array whose first element is the Vitest version that wrote it (see BlobReporter.onTestRunEnd at blob.ts:72-80); a missing version means the file was not produced by the blob reporter.

Source

Thrown at packages/vitest/src/node/reporters/blob.ts:135

  projectsArray: TestProject[],
): Promise<MergedBlobs> {
  // using process.cwd() because --merge-reports can only be used in CLI
  const resolvedDir = resolve(process.cwd(), blobsDirectory)
  const blobsFiles = await readdir(resolvedDir)
  const promises = blobsFiles.map(async (filename) => {
    const fullPath = resolve(resolvedDir, filename)
    const stats = await stat(fullPath)
    if (!stats.isFile()) {
      throw new TypeError(
        `vitest.mergeReports() expects all paths in "${blobsDirectory}" to be files generated by the blob reporter, but "${filename}" is not a file`,
      )
    }
    const content = await readFile(fullPath, 'utf-8')
    const [version, files, errors, coverage, executionTime, environmentModules, transformTime] = parse(
      content,
    ) as MergeReport
    if (!version) {
      throw new TypeError(
        `vitest.mergeReports() expects all paths in "${blobsDirectory}" to be files generated by the blob reporter, but "${filename}" is not a valid blob file`,
      )
    }
    return { version, files, errors, coverage, file: filename, executionTime, environmentModules, transformTime }
  })
  const blobs = await Promise.all(promises)

  if (!blobs.length) {
    throw new Error(
      `vitest.mergeReports() requires at least one blob file in "${blobsDirectory}" directory, but none were found`,
    )
  }

  const versions = new Set(blobs.map(blob => blob.version))
  if (versions.size > 1) {
    throw new Error(
      `vitest.mergeReports() requires all blob files to be generated by the same Vitest version, received\n\n${blobs.map(b => `- "${b.file}" uses v${b.version}`).join('\n')}`,
    )

View on GitHub (pinned to d568f8ce37)

Solutions

  1. Regenerate the blob files by running the blob reporter fresh and merge only those.
  2. Delete any non-blob files from the merge-reports directory before merging.
  3. Ensure the merge-reports directory only contains files written by `BlobReporter` (the default `blob-*.json` outputs).

Example fix

# remove stale/manual files, then regenerate
rm -rf ./blob-reports && vitest --reporter=blob
vitest --merge-reports ./blob-reports
Defensive patterns

Strategy: validation

Validate before calling

import { readdirSync, readFileSync } from 'node:fs'
import { resolve } from 'node:path'
import { parse } from 'flatted'
for (const name of readdirSync(blobsDirectory)) {
  const parsed = parse(readFileSync(resolve(blobsDirectory, name), 'utf-8'))
  if (!Array.isArray(parsed) || !parsed[0]) throw new Error(`${name} is not a valid blob file`)
}

Type guard

import { parse } from 'flatted'
const isBlobFile = (raw: string): boolean => { try { const p = parse(raw); return Array.isArray(p) && !!p[0] } catch { return false } }

Prevention

When it happens

Trigger: Manually placing an arbitrary JSON/text file in the merge-reports directory; copying a partial or truncated blob file; a file written by an older/newer format that lacks the version tuple; a file produced by a different tool that happens to be valid JSON but not a blob report.

Common situations: Mixing manual JSON outputs into the blob directory; a corrupted or half-written blob file from a crashed run; using the wrong directory as the merge-reports source.

Related errors

AI-assisted analysis of vitest-dev/vitest@d568f8ce37 (2026-08-03). Data as JSON: /data/errors/2919417f59e23d95.json. Report an issue: GitHub.