jestjs/jest · error · Error

Attempted to display seed but seed value is undefined

Error message

Attempted to display seed but seed value is undefined

What it means

Thrown by jest-reporters' getSummary() at packages/jest-reporters/src/getSummary.ts:122 when the caller requests seed display (options.showSeed === true) but supplies no seed value (options.seed === undefined). Jest prints a 'Seed: <n>' line in the test summary so that randomized runs can be reproduced; if you ask for that line without giving it a number to print, the function aborts rather than emit a misleading empty seed. It is a hard guard against rendering an undefined value into the summary output.

Source

Thrown at packages/jest-reporters/src/getSummary.ts:122

  const snapshotsUpdated = snapshotResults.updated;
  const suitesFailed = aggregatedResults.numFailedTestSuites;
  const suitesPassed = aggregatedResults.numPassedTestSuites;
  const suitesPending = aggregatedResults.numPendingTestSuites;
  const suitesRun = suitesFailed + suitesPassed;
  const suitesTotal = aggregatedResults.numTotalTestSuites;
  const testsFailed = aggregatedResults.numFailedTests;
  const testsPassed = aggregatedResults.numPassedTests;
  const testsPending = aggregatedResults.numPendingTests;
  const testsTodo = aggregatedResults.numTodoTests;
  const testsTotal = aggregatedResults.numTotalTests;
  const width = (options && options.width) || 0;

  const optionalLines: Array<string> = [];

  if (options?.showSeed === true) {
    const {seed} = options;
    if (seed === undefined) {
      throw new Error('Attempted to display seed but seed value is undefined');
    }
    optionalLines.push(`${chalk.bold('Seed:        ') + seed}`);
  }

  const suites = `${
    chalk.bold('Test Suites: ') +
    (suitesFailed ? `${chalk.bold.red(`${suitesFailed} failed`)}, ` : '') +
    (suitesPending
      ? `${chalk.bold.yellow(`${suitesPending} skipped`)}, `
      : '') +
    (suitesPassed ? `${chalk.bold.green(`${suitesPassed} passed`)}, ` : '') +
    (suitesRun === suitesTotal ? suitesTotal : `${suitesRun} of ${suitesTotal}`)
  } total`;

  const updatedTestsFailed =
    testsFailed + valuesForCurrentTestCases.numFailingTests;
  const updatedTestsPending =
    testsPending + valuesForCurrentTestCases.numPendingTests;

View on GitHub (pinned to 8e6d128e4a)

Solutions

1. Enable randomized ordering so Jest generates and stores a seed: pass --randomize on the CLI or set `randomize: true` in jest.config.js (this auto-populates globalConfig.seed and pairs naturally with --showSeed).
2. Supply an explicit seed: pass --seed=<n> on the CLI or set `seed: <number>` in jest.config.js so globalConfig.seed is defined.
3. Remove `showSeed: true` from your Jest config / reporter options if you do not actually need the Seed line in the summary.
4. If calling getSummary directly in a custom reporter, always pass both together: `{showSeed: globalConfig.showSeed, seed: globalConfig.seed}` and guard `showSeed: Boolean(globalConfig.showSeed) && globalConfig.seed !== undefined` before enabling it.

Example fix

// before (jest.config.js)
module.exports = {
  showSeed: true,
  // no randomize, no seed -> error at getSummary.ts:122
};

// after: enable randomize so a seed is generated
module.exports = {
  randomize: true,
  showSeed: true,
};

// or: pin an explicit seed
module.exports = {
  seed: 12345,
  showSeed: true,
};

// Before calling getSummary, normalise the options so showSeed is only
// true when a numeric seed actually exists.
import type {SummaryOptions} from 'jest-reporters';

function safeSummaryOptions(opts: SummaryOptions): SummaryOptions {
  const showSeed = opts.showSeed === true && typeof opts.seed === 'number';
  return {...opts, showSeed};
}

// usage
const summary = getSummary(aggregatedResults, safeSummaryOptions({
  showSeed: globalConfig.showSeed,
  seed: globalConfig.seed,
  estimatedTime,
}));

// Type + runtime guard narrowing: showSeed truthy implies seed is a number.
type SafeSummaryOptions =
  | ({showSeed?: false} & SummaryOptions)
  | ({showSeed: true; seed: number} & SummaryOptions);

function hasSeed(opts: SummaryOptions): opts is {showSeed: true; seed: number} {
  return opts.showSeed === true && typeof opts.seed === 'number' && Number.isFinite(opts.seed);
}

if (hasSeed(options)) {
  // safe to call getSummary with options.showSeed === true
}

// For custom reporters that wrap getSummary: catch, surface via _setError,
// and re-run without showSeed so the summary still renders.
try {
  message = getSummary(aggregatedResults, {showSeed: true, seed: globalConfig.seed});
} catch (e) {
  this._setError(e as Error);
  message = getSummary(aggregatedResults, {showSeed: false});
}

When it happens

Trigger: Calling getSummary(aggregatedResults, {showSeed: true}) without a numeric seed property. In the CLI/runtime path, SummaryReporter._printTestRunEnd (SummaryReporter.ts:125-129) forwards globalConfig.showSeed and globalConfig.seed, so the error fires when globalConfig.showSeed is true while globalConfig.seed is undefined. Concretely: running jest with --showSeed but no --seed=<n> and no --randomize (which would auto-generate a seed), or setting `showSeed: true` in jest.config without `randomize: true` or `seed: <n>`. Also when invoking getSummary directly from a custom reporter.

Common situations: A developer adds `showSeed: true` to a Jest config or custom reporter to surface the seed for reproducible test ordering, but forgets that a seed is only present when `randomize: true` or an explicit `seed` is configured. Another common case: upgrading Jest and adopting the newer --showSeed flag while the project does not use randomized ordering, leaving globalConfig.seed undefined. Custom reporters that wrap getSummary and hardcode showSeed: true without threading the seed through are the third typical source.

Related errors

• seed value must be between `-0x80000000` and `0x7fffffff` in
• babel-jest: Babel ignores ${chalk.bold(slash(path.relative(c
• Could not find a "package.json" file in ${rootDir}
• ${EXPECTED_COLOR('expected')} value must be a number
• ${RECEIVED_COLOR('received')} value must be a number

AI-assisted analysis of jestjs/jest@8e6d128e4a (2026-08-10). Data as JSON: /api/errors/d71a01efe3608bbe. Report an issue: GitHub.