react19-test-patterns

Name: react19-test-patterns
Author: github

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

INSTALLATION

npx skills add https://github.com/github/awesome-copilot --skill react19-test-patterns

Run in your project or agent environment. Adjust flags if your CLI version differs.

SKILL.md

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>&#x26;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