react19-test-patterns

by github

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 https://github.com/github/awesome-copilot --skill react19-test-patterns Download ZIPGitHub36.2k

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:

• act import fix first, it unblocks everything else

• Simulate → fireEvent fix immediately after act

• Full react-dom/test-utils cleanup remove remaining imports

• StrictMode call counts measure actual, don't guess

• Async act wrapping for remaining "not wrapped in act" warnings

• Custom render helper verify once per codebase, not per test

1. act() Import Fix

// 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

2. Simulate → fireEvent

// 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 });

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:

# 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