Do you want to request a feature or report a bug?

bug

What is the current behavior?

In shallow renderer, The returned callback from useCallback is not the same one between two rerendering even though the dependencies are the same. But useMemo will work as expected.

For example, the following test won't work:

    function SomeComponent() {
      const noop = React.useCallback(() => {}, []);

      return (
        <div onClick={noop} />
      );
    }

    const shallowRenderer = createRenderer();
    let firstResult = shallowRenderer.render(<SomeComponent />);
    let secondResult = shallowRenderer.render(<SomeComponent />);

    expect(firstResult).toEqual(secondResult);

If useCallback returned the same callback between two rendering (I think) the assertion should pass.

but the same (almost) logic will work with useMemo, in the shallow renderer test suite (See https://github.com/facebook/react/blob/master/packages/react-test-renderer/src/__tests__/ReactShallowRendererHooks-test.js#L273-L291).

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Paste the link to your JSFiddle (https://jsfiddle.net/Luktwrdm/) or CodeSandbox (https://codesandbox.io/s/new) example below:

I created a branch in https://github.com/chenesan/react/tree/usecallback-not-work-properly-in-shallow-renderer and you can run the failed shallow renderer test in chenesan@b2dff28#diff-d9a78422c03941578ae9ba487e8132cb .

What is the expected behavior?

useCallback should return the memoized callback when the dependencies unchanged even in shallow renderer.

I tried to look into this and I found out that in shallow renderer useCallback just returns the original callback argument (See https://github.com/facebook/react/blob/master/packages/react-test-renderer/src/ReactShallowRenderer.js#L365-L371) but useMemo will compare the dependencies between rendering. I'm not sure if it's intended (So it's expected that useCallback will not memoize callback in shallow renderer). If it's triaged as a bug I'm glad to send a pr for this :)

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?

react@16.8.6