It seems like react-is v16.6 no longer is compatible with React v16.3 - v16.5, in that React v16.3 - v16.5 will use `Symbol(react.async_mode)`, but `react-is`'s `AsyncMode` export will instead be `Symbol(react.concurrent_mode)`.

It seems like the async mode symbol needs to remain the same in react-is 16.6+, and the `isAsyncMode` function would need to check *both* the AsyncMode and ConcurrentMode symbols.
});
  it('should identify async mode', () => {
    expect(ReactIs.typeOf(<React.unstable_ConcurrentMode />)).toBe(
      ReactIs.ConcurrentMode,
    );
    expect(ReactIs.isConcurrentMode(<React.unstable_ConcurrentMode />)).toBe(
      true,
    );
    expect(ReactIs.isConcurrentMode({type: ReactIs.ConcurrentMode})).toBe(
      false,
    );
    expect(ReactIs.isConcurrentMode(<React.StrictMode />)).toBe(false);
    expect(ReactIs.isConcurrentMode(<div />)).toBe(false);
  });
  it('should identify context consumers', () => {
    const Context = React.createContext(false);
    expect(ReactIs.typeOf(<Context.Consumer />)).toBe(ReactIs.ContextConsumer);
    expect(ReactIs.isContextConsumer(<Context.Consumer />)).toBe(true);
    expect(ReactIs.isContextConsumer(<Context.Provider />)).toBe(false);
    expect(ReactIs.isContextConsumer(<div />)).toBe(false);
  });
  it('should identify context providers', () => {
    const Context = React.createContext(false);
    expect(ReactIs.typeOf(<Context.Provider />)).toBe(ReactIs.ContextProvider);
    expect(ReactIs.isContextProvider(<Context.Provider />)).toBe(true);
    expect(ReactIs.isContextProvider(<Context.Consumer />)).toBe(false);
    expect(ReactIs.isContextProvider(<div />)).toBe(false);
  });
  it('should identify elements', () => {
    expect(ReactIs.typeOf(<div />)).toBe(ReactIs.Element);