Just about every time I set up a new `Context.Provider`, I end up accidentally specifying a `values` prop rather than `value`.  While it's a minor error, generally I build the container in which the provider resides and commit it to the code base before I ever use it.  It's only later when I go to use it that I realize I did it again.  Since the `Context.Provider` seems pretty much useless without a `value` prop specified, I'd love it if there was a prop error if it is missing... especially if another prop is defined on the `Context.Provider` instead.
render() {
        return <div ref="baz" />;
      }
    }
    ReactTestRenderer.create(<Baz />);
    expect(() => ReactTestRenderer.create(<Foo />)).toErrorDev(
      'Warning: Function components cannot be given refs. Attempts ' +
        'to access this ref will fail. ' +
        'Did you mean to use React.forwardRef()?\n\n' +
        'Check the render method of `Foo`.\n' +
        '    in Bar (at **)\n' +
        '    in Foo (at **)',
    );
  });
  it('allows an optional createNodeMock function', () => {
    const mockDivInstance = {appendChild: () => {}};
    const mockInputInstance = {focus: () => {}};
    const mockListItemInstance = {click: () => {}};
    const mockAnchorInstance = {hover: () => {}};
    const log = [];
    class Foo extends React.Component {
      componentDidMount() {
        log.push(this.refs.bar);
      }
      render() {
        return <a ref="bar">Hello, world</a>;
      }
    }
    function createNodeMock(element) {