Provides before/after patterns for migrating test files to React 19 compatibility, including act() imports, Simulate removal, and StrictMode call count changes.

React 19 Test Migration Patterns Reference for all test file migrations required by React 19. Priority Order Fix test files in this order; each layer depends on the previous: 1. act import fix first, it unblocks everything else 2. Simulate → fireEvent fix immediately after act 3. Full react dom/test utils cleanup remove remaining imports 4. StrictMode call counts measure actual, don't guess 5. Async act wrapping for remaining "not wrapped in act" warnings 6. Custom render helper verify once per codebase, not per test 1. act() Import Fix If mixed with other test utils imports: 2. Simulate → fireEvent 3. react dom/test utils Full API Map Old (react dom/test utils) New location act import { act } from 'react' Simulate fireEvent from @testing library/react renderIntoDocument render from @testing library/react findRenderedDOMComponentWithTag getByRole , getByTestId from RTL findRenderedDOMComponentWithClass getByRole or container.querySelector scryRenderedDOMComponentsWithTag getAllByRole from RTL isElement , isCompositeComponent Remove not needed with RTL isDOMComponent Remove 4. StrictMode Call Count Fixes React 19 StrictMode no longer double invokes useEffect in development. Spy assertions counting effect calls must be updated. Strategy always measure, never guess:

react19-test-patterns