Jest
Jest is a JavaScript testing framework for defining, running, and asserting automated tests.
The Art of Unit Testing 3e
Jest is a JavaScript testing framework that provides facilities for writing, running, and reporting tests.
- How it is used
- Provides a single framework for writing, asserting, running, and reporting JavaScript tests.
- How deep it goes
- Explains setup, execution reports, test structure, reuse trade-offs, reporting adapters, and dynamic module fakes.
- Examples
- Uses Hello World test output and a Password Verifier that stubs configuration while verifying logger calls.
- What you can do after
- Apply it via Jest to run tests, interpret failures, watch changes, organize tests, and fake directly imported modules.
Bootstrapping Microservices, Second Edition: With Docker, Kubernetes, GitHub Actions, and Terraform
Jest is a JavaScript testing framework for running automated tests.
- How it is used
- Runs automated JavaScript tests for libraries and individual microservices.
- How deep it goes
- Works through installation, configuration, test execution, and mocked microservice unit tests; leaves Jest’s wider API unexplored.
- Examples
- Uses a math library test and metadata microservice tests for startup and database-backed route behavior.
- What you can do after
- Apply it via Jest to run and watch JavaScript tests and isolate a microservice from its server and database.
Modern Angular
Jest is a JavaScript testing framework and test runner for executing automated tests, typically in a Node.js environment.
- How it is used
- Executes Angular unit tests and reports their results within a Node.js-based testing environment.
- How deep it goes
- Provides setup files, project configuration, lifecycle structure, and component examples, but defers comprehensive service and browser-API testing.
- Examples
- Uses AppComponent specs, TestBed fixtures, ng test, configuration files, HttpClient failures, and Karma-to-Jest migration exercises.
- What you can do after
- Operate Jest through Angular configuration, run specs with ng test, and migrate existing Karma-based tests while diagnosing setup failures.
Contract Testing in Action
Jest is a JavaScript testing framework that provides test structure, assertions, and test execution utilities.
- How it is used
- Uses Jest to structure and execute consumer-driven contract tests for web APIs and event-message consumers.
- How deep it goes
- Explains describe, test, asynchronous execution, and assertions through a complete Pact example, without detailing Jest internals.
- Examples
- Uses nested Movies API scenarios, a GET /movies interaction, a movie response body, generated pact JSON, and an npm test script.
- What you can do after
- Apply it via Jest to write, run, and assert consumer contract tests against Pact mock providers.
Essential TypeScript 5, Third Edition
Jest is a JavaScript testing framework that provides APIs for defining tests, making assertions, and reporting results.
- How it is used
- Supports unit testing for TypeScript application functions and reports whether their runtime behavior matches expectations.
- How deep it goes
- Explains installation, configuration, test construction, matchers, watch mode, failure output, and test-versus-code correction.
- Examples
- Uses a calc.test.ts test for sum(10, 20, 30), Jest matcher examples, watch-mode output, and an intentionally incorrect calculation.
- What you can do after
- Apply it via Jest, ts-jest, and watch mode to create, run, inspect, and repair TypeScript unit tests.
Read how Essential TypeScript 5, Third Edition explains Jest →
Related concepts
- test automation frameworkkind of · A test automation framework is software infrastructure that provides conventions and facilities for defining, organizing, executing, and evaluating automated tests.
- test runnerkind of · A test runner is software that discovers or receives automated tests, executes them, and reports their results.
- Karmaalternative to · Karma is a JavaScript test runner that executes tests in browsers or browser-like environments and reports their results.
- testuses · A test is a procedure or check that evaluates behavior using specified inputs or evidence against expected results or criteria.
- npxused by · npx is an npm command-line package runner that executes package-provided binaries from local dependencies or downloads packages when needed, without requiring global installation.
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