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.
componentWillUnmount() {
        count++;
      }
      render() {
        return <div />;
      }
    }
    const inst = ReactTestRenderer.create(
      <div>
        <Foo />
      </div>,
      {
        createNodeMock: () => 'foo',
      },
    );
    expect(() => inst.unmount()).not.toThrow();
    expect(count).toEqual(1);
  });
  it('supports updates when using refs', () => {
    const log = [];
    const createNodeMock = element => {
      log.push(element.type);
      return element.type;
    };
    class Foo extends React.Component {