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SKILL.md
npx skills add github/awesome-copilot --skill react19-test-patterns
Provides before/after patterns for migrating test files to React 19 compatibility, including act() imports, Simulate removal, and StrictMode call count changes.
npx skills add github/awesome-copilot --skill react19-test-patterns
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 actIf mixed with other test-utils imports:
| 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:
// 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 });# 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