After a discussion with @spicyj we decided to keep the warning even though the functions will throw in production. The warning is the only way to learn about that.

We should also document how to pass the secret through in case you know what you're doing.

function Engineer() {}
      Engineer.prototype = new Person();
      typeCheckPass(PropTypes.instanceOf(Person), new Person());
      typeCheckPass(PropTypes.instanceOf(Person), new Engineer());
      typeCheckPass(PropTypes.instanceOf(Date), new Date());
      typeCheckPass(PropTypes.instanceOf(RegExp), /please/);
    });
    it('should be implicitly optional and not warn without values', () => {
      typeCheckPass(PropTypes.instanceOf(String), null);
      typeCheckPass(PropTypes.instanceOf(String), undefined);
    });
    it('should warn for missing required values', () => {
      typeCheckFailRequiredValues(PropTypes.instanceOf(String).isRequired);
    });
  });
  describe('React Component Types', () => {
    beforeEach(() => {
      MyComponent = class extends React.Component {
        render() {