react19-test-patterns

npx skills add github/awesome-copilot --skill react19-test-patterns --agent copilot

Same command for any agent — swap --agent for claude-code, codex, cursor.

# 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: 1. **`act` import** fix first, it unblocks everything else 2. **`Simulate` → `fireEvent`** fix immediately after act 3. **Full react-dom/test-utils cleanup** remove remaining imports 4. **StrictMode call counts** measure actual, don't guess 5. **Async act wrapping** for remaining "not wrapped in act" warnings 6. **Custom render helper** verify once per codebase, not per test --- ## 1. act() Import Fix ```jsx // Before REMOVED in React 19: import { act } from 'react-dom/test-utils'; // After: import { act } from 'react'; ``` If mixed with other test-utils imports: ```jsx // 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 ```jsx // Before Simulate REMOVED in React 19: import { Simulate } from 'react-dom/test-utils'; Simulate.click(element); Simulate.change(input, { target: { value: '

Run the failing test, read the actual count from the error:
npm test -- --watchAll=false --testPathPattern="[filename]" --forceExit 2>&1 | grep -E "Expected|Received"