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 portals', () => {
    const div = document.createElement('div');
    const portal = ReactDOM.createPortal(<div />, div);
    expect(ReactIs.typeOf(portal)).toBe(ReactIs.Portal);
    expect(ReactIs.isPortal(portal)).toBe(true);
    expect(ReactIs.isPortal(div)).toBe(false);
  });
  it('should identify strict mode', () => {
    expect(ReactIs.typeOf(<React.StrictMode />)).toBe(ReactIs.StrictMode);
    expect(ReactIs.isStrictMode(<React.StrictMode />)).toBe(true);
    expect(ReactIs.isStrictMode({type: ReactIs.StrictMode})).toBe(false);
    expect(ReactIs.isStrictMode(<React.unstable_ConcurrentMode />)).toBe(false);
    expect(ReactIs.isStrictMode(<div />)).toBe(false);
  });
  it('should identify profile root', () => {
    expect(
      ReactIs.typeOf(<React.unstable_Profiler id="foo" onRender={jest.fn()} />),
    ).toBe(ReactIs.Profiler);
    expect(
      ReactIs.isProfiler(
        <React.unstable_Profiler id="foo" onRender={jest.fn()} />,
      ),
    ).toBe(true);
    expect(ReactIs.isProfiler({type: ReactIs.unstable_Profiler})).toBe(false);
    expect(ReactIs.isProfiler(<React.unstable_ConcurrentMode />)).toBe(false);
    expect(ReactIs.isProfiler(<div />)).toBe(false);
  });
});