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.

return <div />;
        },
      });
    });
    it('should warn for invalid values', function() {
      var failMessage = 'Invalid prop `testProp` supplied to ' +
        '`testComponent`, expected a ReactNode.';
      typeCheckFail(PropTypes.node, true, failMessage);
      typeCheckFail(PropTypes.node, function() {}, failMessage);
      typeCheckFail(PropTypes.node, {key: function() {}}, failMessage);
      typeCheckFail(PropTypes.node, {key: <div />}, failMessage);
    });
    it('should not warn for valid values', function() {
      spyOn(console, 'error');
      typeCheckPass(PropTypes.node, <div />);
      typeCheckPass(PropTypes.node, false);
      typeCheckPass(PropTypes.node, <MyComponent />);
      typeCheckPass(PropTypes.node, 'Some string');
      typeCheckPass(PropTypes.node, []);
      typeCheckPass(PropTypes.node, [
        123,
        'Some string',
        <div />,
        ['Another string', [456], <span />, <MyComponent />],
        <MyComponent />,
      ]);
      
      var frag = ReactFragment.create;
      typeCheckPass(PropTypes.node, frag({
        k0: 123,