jestjs/jest · error · Error

Missing second argument. It must be a callback function.

Error message

Missing second argument. It must be a callback function.

What it means

describe() requires exactly two arguments: a description and a callback. Env.ts:399-403 throws when the second argument (specDefinitions) is undefined — i.e. describe was called with only a name. This catches a common typo before the suite is built.

Source

Thrown at packages/jest-jasmine2/src/jasmine/Env.ts:400

          id: getNextSuiteId(),
          description,
          parentSuite: currentDeclarationSuite,
          throwOnExpectationFailure,
          getTestPath() {
            return j$.testPath;
          },
        });

        return suite;
      };

      this.describe = function (
        description: Circus.TestNameLike,
        specDefinitions,
      ) {
        const suite = suiteFactory(description);
        if (specDefinitions === undefined) {
          throw new Error(
            'Missing second argument. It must be a callback function.',
          );
        }
        if (typeof specDefinitions !== 'function') {
          throw new TypeError(
            `Invalid second argument, ${specDefinitions}. It must be a callback function.`,
          );
        }
        if (specDefinitions.length > 0) {
          throw new Error('describe does not expect any arguments');
        }
        if (currentDeclarationSuite.markedPending) {
          suite.pend();
        }
        if (currentDeclarationSuite.markedTodo) {
          // @ts-expect-error TODO Possible error: Suite does not have todo method
          suite.todo();
        }

View on GitHub (pinned to f49721c78e)

Solutions

1. Provide the required callback: describe('name', () => { ... }).
2. If you intended a placeholder suite, use an empty callback describe('name', () => {}) or skip it.
3. Remove the incomplete describe line entirely if it is leftover scaffolding.

Example fix

// before
describe('calculator');

// after
describe('calculator', () => { it('adds', () => {}); });

function assertDescribeArgs(name: unknown, fn: unknown) {
  if (fn === undefined) throw new Error('describe requires a callback as the 2nd argument');
}

function isDescribeArgs(args: [unknown, unknown]): args is [string, () => void] {
  return args.length >= 2 && typeof args[1] === 'function';
}

When it happens

Trigger: Calling `describe('name')` with no callback, or `describe('name', undefined)`. The check at Env.ts:399 (`specDefinitions === undefined`) triggers the throw at line 400.

Common situations: Incomplete test draft left in a file; refactor that removed the body but left the describe line; copy-paste missing the callback; accidental semicolon terminating the call.

Related errors

• Invalid second argument, ${specDefinitions}. It must be a ca
• describe does not expect any arguments
• Missing second argument. It must be a callback function. Per
• Invalid second argument, ${fn}. It must be a callback functi
• Tests cannot be nested. Test "${spec.description}" cannot ru

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/d606d900a1c76804.json. Report an issue: GitHub.