What causes "A "describe" callback must not return a value." in jestjs/jest?

Wrap the callback body in curly braces so calls are statements, not the return value (describe('x', () => { test(...); }).

jestjs/jest · error · ErrorWithStack

A "describe" callback must not return a value.

Error message

A "describe" callback must not return a value.

What it means

After invoking the describe callback, _dispatchDescribe also rejects any non-undefined, non-Promise return value (index.ts:83-87). The callback is meant only to register tests and hooks as a side effect; returning a value is almost always a typo (an accidental arrow-function shorthand return) that would silently lose the intended side effect.

Solutions

Wrap the callback body in curly braces so calls are statements, not the return value (describe('x', () => { test(...); }).
Audit the describe callback for any return/implicit-return of an expression and convert to void or statement form.
If you genuinely need the value, move it into a hook or a variable assignment.

Example fix

// before
describe('math', () =>
  test('adds', () => expect(1 + 1).toBe(2)));
// after
describe('math', () => {
  test('adds', () => expect(1 + 1).toBe(2));
});

Defensive patterns

Strategy: validation

Validate before calling

// Reject describe callbacks whose return type is non-void statically (TS):
// type SyncDescribeFn = () => void;
function registerDescribe(name: string, fn: () => void) {
  describe(name, fn);
}
registerDescribe('x', () => { test('y', () => {}); }); // OK
// registerDescribe('x', () => test('y', () => {})); // TS error: not assignable to () => void

Type guard

function returnsVoid(fn: (...args: any[]) => unknown): boolean {
  // static check via TS is preferred; runtime heuristic for audits:
  return fn.constructor.name !== 'AsyncFunction';
}

Prevention

Type describe callbacks explicitly as () => void so implicit returns become TS errors.
Always wrap describe callback bodies in curly braces.
Run tsc --noImplicitReturns or enable the corresponding lint to catch implicit returns.

When it happens

Trigger: Writing describe('x', () => test('y', () => {})) where the arrow implicitly returns the result of test(); any describe callback using the concise arrow body form that evaluates an expression; describe.each with a callback that returns a value.

Common situations: Accidentally dropping the braces on an arrow function inside describe so it returns test(...) instead of calling it as a statement; refactoring a callback from braces to expression form; copy-paste from a function that returns a value.

Related errors

AI-assisted analysis of jestjs/jest@8e6d128e4a (2026-08-10). Data as JSON: /api/errors/60caa7fcd816f695. Report an issue: GitHub.

Appendix: source

Thrown at packages/jest-circus/src/index.ts:84

    asyncError.message = (error as Error).message;
    throw asyncError;
  }

  dispatchSync({
    asyncError,
    blockName,
    mode,
    name: 'start_describe_definition',
  });
  const describeReturn = blockFn();

  if (isPromise(describeReturn)) {
    throw new ErrorWithStack(
      'Returning a Promise from "describe" is not supported. Tests must be defined synchronously.',
      describeFn,
    );
  } else if (describeReturn !== undefined) {
    throw new ErrorWithStack(
      'A "describe" callback must not return a value.',
      describeFn,
    );
  }

  dispatchSync({blockName, mode, name: 'finish_describe_definition'});
};

const _addHook = (
  fn: Circus.HookFn,
  hookType: Circus.HookType,
  hookFn: THook,
  timeout?: number,
) => {
  const asyncError = new ErrorWithStack(undefined, hookFn);

  if (typeof fn !== 'function') {
    asyncError.message =

View on GitHub (pinned to 8e6d128e4a)