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 {
            next: function() {
              var done = ++i > 2;
              return {value: done ? undefined : ['#' + i, <MyComponent />], done: done};
            },
          };
        },
      };
      iterable.entries = iterable['@@iterator'];
      typeCheckPass(PropTypes.node, iterable);
    });
    it('should not warn for null/undefined if not required', function() {
      typeCheckPass(PropTypes.node, null);
      typeCheckPass(PropTypes.node, undefined);
    });
    it('should warn for missing required values', function() {
      typeCheckFail(
        PropTypes.node.isRequired,
        null,
        'Required prop `testProp` was not specified in `testComponent`.'
      );
      typeCheckFail(
        PropTypes.node.isRequired,
        undefined,
        'Required prop `testProp` was not specified in `testComponent`.'
      );
    });
    it('should accept empty array for required props', function() {
      typeCheckPass(PropTypes.node.isRequired, []);
    });