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.

var props = {testProp: value};
  var error = declaration(
    props,
    'testProp',
    'testComponent',
    ReactPropTypeLocations.prop
  );
  expect(error instanceof Error).toBe(true);
  expect(error.message).toBe(message);
}
function typeCheckPass(declaration, value) {