Repro: https://codesandbox.io/s/fast-water-4i4jb

Notice the flash. I'd expect `suspended` to be `true` during the high pri render.
act(() => setStateFn(state => ({count: state.count + 1})));
      expect(renderer.toJSON()).toEqual({
        type: 'div',
        props: {},
        children: ['count:', '11'],
      });
    }
  });
  it('should support overriding suspense in legacy mode', () => {
    if (__DEV__) {
      
      setSuspenseHandler(() => true);
    }
    function MyComponent() {
      return 'Done';
    }
    const renderer = ReactTestRenderer.create(
      <div>
        <React.Suspense fallback={'Loading'}>
          <MyComponent />
        </React.Suspense>
      </div>,
    );
    const fiber = renderer.root._currentFiber().child;
    if (__DEV__) {
      
      expect(renderer.toJSON().children).toEqual(['Loading']);
      scheduleUpdate(fiber); 
      expect(renderer.toJSON().children).toEqual(['Loading']);