Write JavaScript and TypeScript tests with Jest using consistent structure, dependency mocking, and checks for asynchronous code. Includes guidance for snapshots and React components, focusing on user interactions, accessibility, and choosing appropriate assertions for expected results.
Best practices for writing JavaScript/TypeScript tests using Jest, including mocking strategies, test structure, and common patterns.
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.test.ts or .test.js suffix__tests__ directorydescribe('Component/Function/Class', () => { it('should do something', () => {}) })jest.mock() for module-level mocksjest.spyOn() for specific function mocksmockImplementation() or mockReturnValue() to define mock behaviorjest.resetAllMocks() in afterEachresolves/rejects matchers for promisesjest.setTimeout()userEvent over fireEvent for more realistic user interactionsexpect(value).toBe(expected), expect(value).toEqual(expected)expect(value).toBeTruthy(), expect(value).toBeFalsy()expect(value).toBeGreaterThan(3), expect(value).toBeLessThanOrEqual(3)expect(value).toMatch(/pattern/), expect(value).toContain('substring')expect(array).toContain(item), expect(array).toHaveLength(3)expect(object).toHaveProperty('key', value)expect(fn).toThrow(), expect(fn).toThrow(Error)expect(mockFn).toHaveBeenCalled(), expect(mockFn).toHaveBeenCalledWith(arg1, arg2)No reviews yet. Tell others what you thought.
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