Provides before/after patterns for migrating test files to React 19 compatibility, including act() imports, Simulate removal, and StrictMode call count changes.
Reference for all test file migrations required by React 19.
Fix test files in this order; each layer depends on the previous:
act import fix first, it unblocks everything elseSimulate → fireEvent fix immediately after act// Before REMOVED in React 19:
import { act } from 'react-dom/test-utils';
// After:
import { act } from 'react';
If mixed with other test-utils imports:
// Before:
import { act, Simulate, renderIntoDocument } from 'react-dom/test-utils';
// After split the imports:
import { act } from 'react';
import { fireEvent, render } from '@testing-library/react'; // replaces Simulate + renderIntoDocument
// Before Simulate REMOVED in React 19:
import { Simulate } from 'react-dom/test-utils';
Simulate.click(element);
Simulate.change(input, { target: { value: 'hello' } });
Simulate.submit(form);
Simulate.keyDown(element, { key: 'Enter', keyCode: 13 });
// After:
import { fireEvent } from '@testing-library/react';
fireEvent.click(element);
fireEvent.change(input, { target: { value: 'hello' } });
fireEvent.submit(form);
fireEvent.keyDown(element, { key: 'Enter', keyCode: 13 });
| 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 |
React 19 StrictMode no longer double-invokes useEffect in development. Spy assertions counting effect calls must be updated.
Strategy always measure, never guess:
# Run the failing test, read the actual count from the error:
npm test -- --watchAll=false --testPathPattern="[filename]" --forceExit 2>&1 | grep -E "Expected|Received"
// Before (React 18 StrictMode effects ran twice):
expect(mockFn).toHaveBeenCalledTimes(2); // 1 call × 2 (strict double-invoke)
// After (React 19 StrictMode effects run once):
expect(mockFn).toHaveBeenCalledTimes(1);
// Render-phase calls (component body) still double-invoked in React 19 StrictMode:
expect(renderSpy).toHaveBeenCalledTimes(2); // stays at 2 for render body calls