A warning is thrown because of an update to ForwardRef when testing a component animated with react-spring with @testing-library/react

Question

I have a component animated with react-spring using the useSpring hook. Something like:

function Toggle({ handleToggle, toggled }) {
  const x = useSpring({
    x: toggled ? 1 : 0
  });
  return (
    <div className={styles.switch} onToggle={handleToggle} data-testid="switch">
      <animated.div
        className={styles.circle}
        style={{
          transform: x
            .interpolate({
              range: [0, 0.4, 0.8, 1],
              output: [0, 5, 10, 16]
            })
            .interpolate((x) => `translateX(${x}px)`)
        }}>
        &nbsp;
      </animated.div>
    </div>
  );
}

When testing the component a warning is thrown:

Warning: An update to ForwardRef inside a test was not wrapped in act(...).

      When testing, code that causes React state updates should be wrapped into act(...):

      act(() => {
        /* fire events that update state */
      });
      /* assert on the output */

      This ensures that you're testing the behavior the user would see in the browser. Learn more at https://reactjs.org/docs/test-utils.html#act
          in ForwardRef (created by Toggle)
          in Toggle

The code for my test is:

test("Toggle works", () => {
    let toggled = false;
    const handleToggle = jest.fn(() => {
      toggled = true;
    });
    const { getByTestId, queryByTestId } = render(
      <Toggle toggled={toggled} handleToggle={handleToggle}/>
    );
  });

How should I test components animated with react-spring using @testing-library/react?

Hi, did you ever resolve this? – lukehillonline May 22 '20 at 16:21 — lukehillonline, May 22 '20 at 16:21

score 3 · Accepted Answer · answered Dec 17 '20 at 19:52

I had this warning while testing a component that uses useSpring and <animated.div> in a react-test-renderer renderer snapshot creation:

import renderer from 'react-test-renderer';
//(...)
  it('matches snapshot', () => {
    const tree = renderer.create(<Component />).toJSON();
    expect(tree).toMatchSnapshot();
  });
//(...)

I've found inspiration in this link, and could solve it just by adding the Jest's useFakeTimers call:

import renderer from 'react-test-renderer';
//(...)
  it('matches snapshot', () => {
    jest.useFakeTimers(); //ADDED
    const tree = renderer.create(<Component />).toJSON();
    expect(tree).toMatchSnapshot();
  });
//(...)

See that wrapping stuff with act, like in the referenced link, was not necessary in this case.

While researching I also found this following blog post, that explains the reasons and describes some cases in which this warning is shown, including a case when you do use jest.useFakeTimers(), the warning keeps being displayed and using act is necessary: Fix the "not wrapped in act(...)" warning

A warning is thrown because of an update to ForwardRef when testing a component animated with react-spring with @testing-library/react

1 Answers1