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.

});
  describe('ObjectOf Type', function() {
    it('should fail for invalid argument', function() {
      typeCheckFail(
        PropTypes.objectOf({ foo: PropTypes.string }),
        { foo: 'bar' },
        'Property `testProp` of component `testComponent` has invalid PropType notation inside objectOf.'
      );
    });
    it('should support the objectOf propTypes', function() {
      typeCheckPass(PropTypes.objectOf(PropTypes.number), {a: 1, b: 2, c: 3});
      typeCheckPass(
        PropTypes.objectOf(PropTypes.string),
        {a: 'a', b: 'b', c: 'c'}
      );
      typeCheckPass(
        PropTypes.objectOf(PropTypes.oneOf(['a', 'b'])),
        {a: 'a', b: 'b'}
      );
      typeCheckPass(
        PropTypes.objectOf(PropTypes.symbol),
        {a: Symbol(), b: Symbol(), c: Symbol()}
      );
    });
    it('should support objectOf with complex types', function() {
      typeCheckPass(
        PropTypes.objectOf(PropTypes.shape({a: PropTypes.number.isRequired})),
        {a: {a: 1}, b: {a: 2}}
      );
      function Thing() {}