javascript-typescript-jest
Best practices for writing JavaScript/TypeScript tests using Jest, including mocking strategies, test structure, and common patterns.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/github/awesome-copilot --skill javascript-typescript-jest- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads javascript-typescript-jest automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
Test Structure
- Name test files with
.test.tsor.test.jssuffix - Place test files next to the code they test or in a dedicated
__tests__directory - Use descriptive test names that explain the expected behavior
- Use nested describe blocks to organize related tests
- Follow the pattern:
describe('Component/Function/Class', () => { it('should do something', () => {}) })
Effective Mocking
- Mock external dependencies (APIs, databases, etc.) to isolate your tests
- Use
jest.mock()for module-level mocks - Use
jest.spyOn()for specific function mocks - Use
mockImplementation()ormockReturnValue()to define mock behavior - Reset mocks between tests with
jest.resetAllMocks()inafterEach
Testing Async Code
- Always return promises or use async/await syntax in tests
- Use
resolves/rejectsmatchers for promises - Set appropriate timeouts for slow tests with
jest.setTimeout()
Snapshot Testing
- Use snapshot tests for UI components or complex objects that change infrequently
- Keep snapshots small and focused
- Review snapshot changes carefully before committing
Testing React Components
- Use React Testing Library over Enzyme for testing components
- Test user behavior and component accessibility
- Query elements by accessibility roles, labels, or text content
- Use
userEventoverfireEventfor more realistic user interactions
Common Jest Matchers
- Basic:
expect(value).toBe(expected),expect(value).toEqual(expected) - Truthiness:
expect(value).toBeTruthy(),expect(value).toBeFalsy() - Numbers:
expect(value).toBeGreaterThan(3),expect(value).toBeLessThanOrEqual(3) - Strings:
expect(value).toMatch(/pattern/),expect(value).toContain('substring') - Arrays:
expect(array).toContain(item),expect(array).toHaveLength(3) - Objects:
expect(object).toHaveProperty('key', value) - Exceptions:
expect(fn).toThrow(),expect(fn).toThrow(Error) - Mock functions:
expect(mockFn).toHaveBeenCalled(),expect(mockFn).toHaveBeenCalledWith(arg1, arg2)
FAQ
What does the javascript-typescript-jest skill do?
Best practices for writing JavaScript/TypeScript tests using Jest, including mocking strategies, test structure, and common patterns.
How do I install javascript-typescript-jest?
Run npx skills add https://github.com/github/awesome-copilot --skill javascript-typescript-jest in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/javascript-typescript-jest/ (personal) or .claude/skills/javascript-typescript-jest/ (project).
Which AI agents can use javascript-typescript-jest?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is javascript-typescript-jest safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; Runlayer flagged items to review; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains javascript-typescript-jest?
It is published by github in github/awesome-copilot, and it is an official skill from the maker of the technology it covers. It has 13,185 recorded installs.
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