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feat(prefer-mocked): add new rule (jest-community#1470)
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‎README.md

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| [prefer-importing-jest-globals](docs/rules/prefer-importing-jest-globals.md) | Prefer importing Jest globals | | | 🔧 | |
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| [prefer-lowercase-title](docs/rules/prefer-lowercase-title.md) | Enforce lowercase test names | | | 🔧 | |
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| [prefer-mock-promise-shorthand](docs/rules/prefer-mock-promise-shorthand.md) | Prefer mock resolved/rejected shorthands for promises | | | 🔧 | |
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| [prefer-mocked](docs/rules/prefer-mocked.md) | Prefer jest.mocked() over (fn as jest.Mock) | | | 🔧 | |
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| [prefer-snapshot-hint](docs/rules/prefer-snapshot-hint.md) | Prefer including a hint with external snapshots | | | | |
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| [prefer-spy-on](docs/rules/prefer-spy-on.md) | Suggest using `jest.spyOn()` | | | 🔧 | |
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| [prefer-strict-equal](docs/rules/prefer-strict-equal.md) | Suggest using `toStrictEqual()` | | | | 💡 |

‎docs/rules/prefer-mocked.md

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# Prefer jest.mocked() over (fn as jest.Mock) (`prefer-mocked`)
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🔧 This rule is automatically fixable by the
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[`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
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<!-- end auto-generated rule header -->
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When working with mocks of functions using Jest, it's recommended to use the
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jest.mocked helper function to properly type the mocked functions. This rule
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enforces the use of jest.mocked for better type safety and readability.
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## Rule details
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The following patterns are warnings:
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```typescript
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(foo as jest.Mock).mockReturnValue(1);
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const mock = (foo as jest.Mock).mockReturnValue(1);
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(foo as unknown as jest.Mock).mockReturnValue(1);
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(Obj.foo as jest.Mock).mockReturnValue(1);
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([].foo as jest.Mock).mockReturnValue(1);
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```
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The following patterns are not warnings:
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```js
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jest.mocked(foo).mockReturnValue(1);
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const mock = jest.mocked(foo).mockReturnValue(1);
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jest.mocked(Obj.foo).mockReturnValue(1);
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jest.mocked([].foo).mockReturnValue(1);
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```

‎src/rules/__tests__/prefer-mocked.test.ts

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import path from 'path';
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import dedent from 'dedent';
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import rule from '../prefer-mocked';
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import { FlatCompatRuleTester as RuleTester } from './test-utils';
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function getFixturesRootDir(): string {
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return path.join(__dirname, 'fixtures');
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}
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const rootPath = getFixturesRootDir();
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const ruleTester = new RuleTester({
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parser: require.resolve('@typescript-eslint/parser'),
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parserOptions: {
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sourceType: 'module',
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tsconfigRootDir: rootPath,
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project: './tsconfig.json',
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},
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});
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ruleTester.run('prefer-mocked', rule, {
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valid: [
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dedent`
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import { foo } from './foo';
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foo();
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`,
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dedent`
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import { foo } from './foo';
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jest.mocked(foo).mockReturnValue(1);
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`,
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dedent`
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import { bar } from './bar';
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bar.mockReturnValue(1);
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`,
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dedent`
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import { foo } from './foo';
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sinon.stub(foo).returns(1);
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`,
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dedent`
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import { foo } from './foo';
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foo.mockImplementation(() => 1);
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`,
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dedent`
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const obj = { foo() {} };
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obj.foo();
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`,
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dedent`
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const mockFn = jest.fn();
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mockFn.mockReturnValue(1);
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`,
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dedent`
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const arr = [() => {}];
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arr[0]();
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`,
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dedent`
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const obj = { foo() {} };
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obj.foo.mockReturnValue(1);
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`,
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dedent`
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const obj = { foo() {} };
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jest.spyOn(obj, 'foo').mockReturnValue(1);
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`,
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dedent`
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type MockType = jest.Mock;
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const mockFn = jest.fn();
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(mockFn as MockType).mockReturnValue(1);
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`,
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],
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invalid: [
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{
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code: dedent`
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import { foo } from './foo';
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(foo as jest.Mock).mockReturnValue(1);
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`,
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output: dedent`
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import { foo } from './foo';
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(jest.mocked(foo)).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 3,
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},
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],
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},
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{
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code: dedent`
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import { foo } from './foo';
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(foo as jest.Mock).mockImplementation(1);
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`,
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output: dedent`
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import { foo } from './foo';
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(jest.mocked(foo)).mockImplementation(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 3,
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},
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],
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},
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{
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code: dedent`
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import { foo } from './foo';
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(foo as unknown as jest.Mock).mockReturnValue(1);
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`,
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output: dedent`
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import { foo } from './foo';
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(jest.mocked(foo)).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 3,
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},
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],
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},
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{
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code: dedent`
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import { Obj } from './foo';
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(Obj.foo as jest.Mock).mockReturnValue(1);
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`,
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output: dedent`
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import { Obj } from './foo';
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(jest.mocked(Obj.foo)).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 3,
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},
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],
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},
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{
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code: dedent`
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([].foo as jest.Mock).mockReturnValue(1);
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`,
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output: dedent`
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(jest.mocked([].foo)).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 1,
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},
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],
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},
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{
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code: dedent`
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import { foo } from './foo';
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(foo as jest.MockedFunction).mockReturnValue(1);
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`,
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output: dedent`
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import { foo } from './foo';
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(jest.mocked(foo)).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 3,
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},
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],
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},
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{
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code: dedent`
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import { foo } from './foo';
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(foo as jest.MockedFunction).mockImplementation(1);
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`,
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output: dedent`
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import { foo } from './foo';
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(jest.mocked(foo)).mockImplementation(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 3,
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},
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],
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},
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{
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code: dedent`
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import { foo } from './foo';
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(foo as unknown as jest.MockedFunction).mockReturnValue(1);
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`,
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output: dedent`
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import { foo } from './foo';
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(jest.mocked(foo)).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 3,
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},
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],
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},
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{
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code: dedent`
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import { Obj } from './foo';
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(Obj.foo as jest.MockedFunction).mockReturnValue(1);
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`,
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output: dedent`
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import { Obj } from './foo';
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(jest.mocked(Obj.foo)).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 3,
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},
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],
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},
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{
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code: dedent`
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(new Array(0).fill(null).foo as jest.MockedFunction).mockReturnValue(1);
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`,
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output: dedent`
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(jest.mocked(new Array(0).fill(null).foo)).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 1,
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},
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],
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},
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{
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code: dedent`
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(jest.fn(() => foo) as jest.MockedFunction).mockReturnValue(1);
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`,
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output: dedent`
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(jest.mocked(jest.fn(() => foo))).mockReturnValue(1);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 2,
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line: 1,
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},
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],
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},
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{
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code: dedent`
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const mockedUseFocused = useFocused as jest.MockedFunction<typeof useFocused>;
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`,
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output: dedent`
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const mockedUseFocused = jest.mocked(useFocused);
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 26,
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line: 1,
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},
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],
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},
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{
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code: dedent`
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const filter = (MessageService.getMessage as jest.Mock).mock.calls[0][0];
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`,
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output: dedent`
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const filter = (jest.mocked(MessageService.getMessage)).mock.calls[0][0];
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`,
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options: [],
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errors: [
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{
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messageId: 'useJestMocked',
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column: 17,
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line: 1,
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},
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],
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},
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],
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});

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