Right now we validate some of our proptype definitions, but we don't surface the issue until that component class is consumed. We should instead validate these, in `__DEV__` only as warnings when the class in created. This means that a call to `React.PropTypes.onOf('foo')` results in an immediate warning logged.

This is a relatively contained bit of code so would be a good candidate for somebody looking to start contributing to React.

'Invalid prop `testProp` of type `regexp` supplied to ' +
        '`testComponent`, expected `string`.'
      );
    });
    it('should not warn for valid values', function() {
      typeCheckPass(PropTypes.array, []);
      typeCheckPass(PropTypes.bool, false);
      typeCheckPass(PropTypes.func, function() {});
      typeCheckPass(PropTypes.number, 0);
      typeCheckPass(PropTypes.string, '');
      typeCheckPass(PropTypes.object, {});
      typeCheckPass(PropTypes.object, new Date());
      typeCheckPass(PropTypes.object, /please/);
      typeCheckPass(PropTypes.symbol, Symbol());
    });
    it('should be implicitly optional and not warn without values', function() {
      typeCheckPass(PropTypes.string, null);
      typeCheckPass(PropTypes.string, undefined);
    });
    it('should warn for missing required values', function() {
      typeCheckFail(PropTypes.string.isRequired, null, requiredMessage);
      typeCheckFail(PropTypes.string.isRequired, undefined, requiredMessage);
    });
  });
  describe('Any type', function() {
    it('should should accept any value', function() {
      typeCheckPass(PropTypes.any, 0);
      typeCheckPass(PropTypes.any, 'str');
      typeCheckPass(PropTypes.any, []);
      typeCheckPass(PropTypes.any, Symbol());