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.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/github/awesome-copilot --skill react19-test-patterns- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads react19-test-patterns automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
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:
actimport fix first, it unblocks everything elseSimulate→fireEventfix 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
FAQ
What does the react19-test-patterns skill do?
Provides before/after patterns for migrating test files to React 19 compatibility, including act() imports, Simulate removal, and StrictMode call count changes.
How do I install react19-test-patterns?
Run npx skills add https://github.com/github/awesome-copilot --skill react19-test-patterns in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/react19-test-patterns/ (personal) or .claude/skills/react19-test-patterns/ (project).
Which AI agents can use react19-test-patterns?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is react19-test-patterns safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains react19-test-patterns?
It is published by github in github/awesome-copilot, and it is an official skill from the maker of the technology it covers. It has 1,211 recorded installs.
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