Change:
expect(root).toMatchRenderedOutput('SiblingB'); }); <ins> it('resolves defaultProps without breaking bailout due to unchanged props and state, #17151', async () => { class LazyImpl extends React.Component { static defaultProps = {value: 0}; render() { const text = `${this.props.label}: ${this.props.value}`; return <Text text={text} />; } } const Lazy = lazy(() => fakeImport(LazyImpl)); const instance1 = React.createRef(null); const instance2 = React.createRef(null); const root = ReactTestRenderer.create( <> <LazyImpl ref={instance1} label="Not lazy" /> <Suspense fallback={<Text text="Loading..." />}> <Lazy ref={instance2} label="Lazy" /> </Suspense> </>, { unstable_isConcurrent: true, }, ); expect(Scheduler).toFlushAndYield(['Not lazy: 0', 'Loading...']); expect(root).not.toMatchRenderedOutput('Not lazy: 0Lazy: 0'); await Promise.resolve(); expect(Scheduler).toFlushAndYield(['Lazy: 0']); expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0'); // Should bailout due to unchanged props and state instance1.current.setState(null); expect(Scheduler).toFlushAndYield([]); expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0'); // Should bailout due to unchanged props and state instance2.current.setState(null); expect(Scheduler).toFlushAndYield([]); expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0'); }); it('resolves defaultProps without breaking bailout in PureComponent, #17151', async () => { class LazyImpl extends React.PureComponent { static defaultProps = {value: 0}; state = {}; render() { const text = `${this.props.label}: ${this.props.value}`; return <Text text={text} />; } } const Lazy = lazy(() => fakeImport(LazyImpl)); const instance1 = React.createRef(null); const instance2 = React.createRef(null); const root = ReactTestRenderer.create( <> <LazyImpl ref={instance1} label="Not lazy" /> <Suspense fallback={<Text text="Loading..." />}> <Lazy ref={instance2} label="Lazy" /> </Suspense> </>, { unstable_isConcurrent: true, }, ); expect(Scheduler).toFlushAndYield(['Not lazy: 0', 'Loading...']); expect(root).not.toMatchRenderedOutput('Not lazy: 0Lazy: 0'); await Promise.resolve(); expect(Scheduler).toFlushAndYield(['Lazy: 0']); expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0'); // Should bailout due to shallow equal props and state instance1.current.setState({}); expect(Scheduler).toFlushAndYield([]); expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0'); // Should bailout due to shallow equal props and state instance2.current.setState({}); expect(Scheduler).toFlushAndYield([]); expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0'); }); </ins> it('sets defaultProps for modern lifecycles', async () => { class C extends React.Component { static defaultProps = {text: 'A'};

Discussion:
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Can you turn this into a failing test please?
Sure.
Send a PR?
OK
Feel free to add a fix if you know where the bug is