Benutzerdefinierte Assertion-Matcher für Next.js-Header- und Redirect-Validierung

expect.extend({
  toHaveHeader(response, headerName, expectedValue) {
    const actualValue = response.headers.get(headerName);
    const pass = expectedValue instanceof RegExp
      ? expectedValue.test(actualValue ?? '')
      : actualValue === expectedValue;
 
    return {
      pass,
      message: () =>
        `Expected header "${headerName}" to ${pass ? 'not ' : ''}match ${expectedValue}, but received "${actualValue}"`,
    };
  },
});