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.
static contextType = Context;
      render() {
        renderedContext = this.context;
        return <div />;
      }
    }
    const firstContext = {foo: 123};
    const secondContext = {bar: 456};
    const container = document.createElement('div');
    ReactDOM.render(
      <Context.Provider value={firstContext}>
        <Component />
      </Context.Provider>,
      container,
    );
    expect(renderedContext).toBe(firstContext);
    ReactDOM.render(
      <Context.Provider value={secondContext}>
        <Component />
      </Context.Provider>,
      container,
    );
    expect(renderedContext).toBe(secondContext);
  });
  it('should warn if both contextType and contextTypes are defined', () => {
    const Context = React.createContext();
    class ParentContextProvider extends React.Component {