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plugins/react19-upgrade/skills/react19-test-patterns/SKILL.md

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+---
+name: react19-test-patterns
+description: 'Provides before/after patterns for migrating test files to React 19 compatibility, including act() imports, Simulate removal, and StrictMode call count changes.'
+---
+
+# 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: '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:**
+```bash
+# Run the failing test, read the actual count from the error:
+npm test -- --watchAll=false --testPathPattern="[filename]" --forceExit 2>&1 | grep -E "Expected|Received"
+```
+
+```jsx
+// 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);
+```
+
+```jsx
+// Render-phase calls (component body)  still double-invoked in React 19 StrictMode:
+expect(renderSpy).toHaveBeenCalledTimes(2);  // stays at 2 for render body calls