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101 lines
3.1 KiB
Markdown
101 lines
3.1 KiB
Markdown
---
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name: react19-test-patterns
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description: '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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---
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# React 19 Test Migration Patterns
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Reference for all test file migrations required by React 19.
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## Priority Order
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Fix test files in this order; each layer depends on the previous:
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1. **`act` import** fix first, it unblocks everything else
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2. **`Simulate` → `fireEvent`** fix immediately after act
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3. **Full react-dom/test-utils cleanup** remove remaining imports
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4. **StrictMode call counts** measure actual, don't guess
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5. **Async act wrapping** for remaining "not wrapped in act" warnings
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6. **Custom render helper** verify once per codebase, not per test
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---
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## 1. act() Import Fix
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```jsx
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// Before REMOVED in React 19:
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import { act } from 'react-dom/test-utils';
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// After:
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import { act } from 'react';
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```
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If mixed with other test-utils imports:
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```jsx
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// Before:
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import { act, Simulate, renderIntoDocument } from 'react-dom/test-utils';
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// After split the imports:
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import { act } from 'react';
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import { fireEvent, render } from '@testing-library/react'; // replaces Simulate + renderIntoDocument
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```
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---
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## 2. Simulate → fireEvent
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```jsx
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// Before Simulate REMOVED in React 19:
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import { Simulate } from 'react-dom/test-utils';
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Simulate.click(element);
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Simulate.change(input, { target: { value: 'hello' } });
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Simulate.submit(form);
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Simulate.keyDown(element, { key: 'Enter', keyCode: 13 });
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// After:
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import { fireEvent } from '@testing-library/react';
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fireEvent.click(element);
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fireEvent.change(input, { target: { value: 'hello' } });
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fireEvent.submit(form);
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fireEvent.keyDown(element, { key: 'Enter', keyCode: 13 });
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```
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---
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## 3. react-dom/test-utils Full API Map
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| Old (react-dom/test-utils) | New location |
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|---|---|
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| `act` | `import { act } from 'react'` |
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| `Simulate` | `fireEvent` from `@testing-library/react` |
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| `renderIntoDocument` | `render` from `@testing-library/react` |
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| `findRenderedDOMComponentWithTag` | `getByRole`, `getByTestId` from RTL |
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| `findRenderedDOMComponentWithClass` | `getByRole` or `container.querySelector` |
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| `scryRenderedDOMComponentsWithTag` | `getAllByRole` from RTL |
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| `isElement`, `isCompositeComponent` | Remove not needed with RTL |
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| `isDOMComponent` | Remove |
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---
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## 4. StrictMode Call Count Fixes
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React 19 StrictMode no longer double-invokes `useEffect` in development. Spy assertions counting effect calls must be updated.
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**Strategy always measure, never guess:**
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```bash
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# Run the failing test, read the actual count from the error:
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npm test -- --watchAll=false --testPathPattern="[filename]" --forceExit 2>&1 | grep -E "Expected|Received"
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```
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```jsx
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// Before (React 18 StrictMode effects ran twice):
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expect(mockFn).toHaveBeenCalledTimes(2); // 1 call × 2 (strict double-invoke)
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// After (React 19 StrictMode effects run once):
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expect(mockFn).toHaveBeenCalledTimes(1);
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```
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```jsx
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// Render-phase calls (component body) still double-invoked in React 19 StrictMode:
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expect(renderSpy).toHaveBeenCalledTimes(2); // stays at 2 for render body calls
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