jestjs/jest · error · Error

${EXPECTED_COLOR('expected')} value must be a string or regu

Error message

${EXPECTED_COLOR('expected')} value must be a string or regular expression

What it means

Thrown by `toMatch` (matchers.ts:836) when the expected value is neither a string nor a regex-like object (something with a `.test` function). The matcher branches on string (substring) vs RegExp (pattern); anything else (number, object without test, null, undefined, array) is rejected.

Source

Thrown at packages/expect/src/matchers.ts:837

      isNot: this.isNot,
      promise: this.promise,
    };

    if (typeof received !== 'string') {
      throw new TypeError(
        matcherErrorMessage(
          matcherHint(matcherName, undefined, undefined, options),
          `${RECEIVED_COLOR('received')} value must be a string`,
          printWithType('Received', received, printReceived),
        ),
      );
    }

    if (
      !(typeof expected === 'string') &&
      !(expected && typeof expected.test === 'function')
    ) {
      throw new Error(
        matcherErrorMessage(
          matcherHint(matcherName, undefined, undefined, options),
          `${EXPECTED_COLOR(
            'expected',
          )} value must be a string or regular expression`,
          printWithType('Expected', expected, printExpected),
        ),
      );
    }

    const pass =
      typeof expected === 'string'
        ? received.includes(expected)
        : new RegExp(expected).test(received);

    const message = pass
      ? () =>
          typeof expected === 'string'

View on GitHub (pinned to 8e6d128e4a)

Solutions

1. Pass a string substring or a RegExp: toMatch('hel') or toMatch(/^hel/).
2. Convert a config pattern string into a RegExp when pattern semantics are needed: new RegExp(pattern).
3. Ensure the expected variable is defined (a failed lookup gives undefined).
4. Do not pass plain objects or numbers; use the correct matcher for those types.

Example fix

// before
expect(text).toMatch('*error*'); // treated as literal substring
expect(text).toMatch(404);

// after
expect(text).toMatch('error');
expect(text).toMatch(/error/);
// convert a glob-ish config
expect(text).toMatch(new RegExp(configPattern));

const expected = pattern;
if (typeof expected !== 'string' && !(expected instanceof RegExp)) {
  throw new Error('toMatch expected must be a string or RegExp');
}
expect(text).toMatch(expected);

const isStringOrRegExp = (v: unknown): v is string | RegExp =>
  typeof v === 'string' || v instanceof RegExp;

When it happens

Trigger: Calling `expect('hello').toMatch(5)` (number), `expect('hello').toMatch({pattern: 'h'})` (plain object), `expect('hello').toMatch(null)`, or omitting the expected so it is undefined.

Common situations: Passing a glob or pattern string from a config and forgetting it must be a RegExp for pattern semantics; passing an object by mistake; a variable that is undefined because a lookup failed.

Related errors

• ${RECEIVED_COLOR('received')} value must be a string
• ${EXPECTED_COLOR('expected')} value must be a number
• ${RECEIVED_COLOR('received')} value must be a number
• ${EXPECTED_COLOR('expected')} value must be a function
• ${RECEIVED_COLOR('received')} value must not be null nor und

AI-assisted analysis of jestjs/jest@8e6d128e4a (2026-08-10). Data as JSON: /api/errors/82e64674b1423858. Report an issue: GitHub.