Mastering Jest Testing with TypeScript and Node.js

Access the course repository by downloading the zip or cloning the repo from my GitHub or the resources linked for this lecture.

Set up a TypeScript project with Jest, install ts-jest and types, configure jest and tsconfig, create a sum function and a spec test, then run npm test.

Discover how jest locates tests by default using __tests__ folders or test or spec file names, and run a single file or test case with npm test -- <file>.

Expose the fundamental Jest building blocks, including import, describe, test or it, and expect with toBe and other matchers, while covering test placement and nested describes.

Define the system under test and explain the arrange, act, and assert pattern. Demonstrate how to set up arguments, create Sut, invoke the function, and assert results.

Master unit testing in jest with TypeScript and Node.js by testing utils.ts functions like add, subtract, is even, create user, JWT token, and calculate average, including empty array edge cases.

Explore testing a calculator class in jest, validating initial value zero, add and subtract behavior, and isPositive checks for positive values.

Mastering Jest testing using TypeScript and Node.js teaches how to use lifecycle hooks—before each, after each, before all, and after all—to manage test setup and reduce repetition.

Explore how dummy test doubles in Jest replace real dependencies—functions, classes, and database connections—using a TypeScript book service example to test functionality.

Explore stubs and fakes as test doubles in Jest with TypeScript, wiring an order service to mock inventory and payment gateway, test checkout scenarios without real external calls.

Explore stubs and fakes in action within Jest testing for a Node.js and TypeScript workflow, using a fake payment gateway and inventory stub to validate order processing and decimal handling.

Refactor the test setup to improve readability and maintainability by introducing a transaction type and centralizing setup with beforeEach for fakes like the payment gateway, inventory, and order service.

Learn to use jest.spyOn to create spies on object methods, track calls, and control outputs for async and sync code with mock return value, mock resolved value, and mock implementation.

Clear mocks between tests using restore all mocks to prevent leakage. Set up a role spy with jest spy on get roll in beforeEach and verify mock return values.

Learn how to test the user service’s register user flow by spying on and mocking database and newsletter interactions with jest, preparing for reliable unit tests.

Master Jest spyOn to mock database and newsletter calls, verify create user and subscribe user receive correct data, return a success response, and avoid spinning up real services.

Simulate errors with jest.spyOn() to throw errors across user, database, and newsletter services, using mock implementations and verifying error handling and spy calls.

Explore how to mock modules with jest.mock in TypeScript, using targeted mocks, just marks, and factory callbacks, while comparing mocks and spies and preserving type safety.

Learn to mock external third‑party modules and built‑in node modules with Jest in a TypeScript and Node.js workflow, including fs readFileSync and axios via mock and spy‑on strategies.

Learn how to handle errors in tests by throwing errors and testing error flows, using spies and mocks to simulate services in a Node.js, TypeScript environment.

Learn how to test error handling in Jest with TypeScript and Node by simulating failed database calls, using async rejects and try/catch, and validating error instances and messages.

Explore enterprise level error testing in Jest, using a custom error class with HTTP and app codes, a custom logger, and spies to ensure errors are thrown with precise arguments.

Learn to manage noisy logs in Jest tests by mocking the custom logger or specific log functions. Validate error handling with custom errors, and keep console output clean during tests.

Practice building a TypeScript sha256 hash generator with a salt to produce URL-safe hashes, then set up and run tests and the dev script to verify functionality.

Explore how to write and organize Jest tests in a TypeScript and Node.js project, including setting up test files, coverage, and validating hash generator behavior with various inputs and salts.

Understand code coverage metrics in Jest testing, including lines, functions, and branches, and learn to set thresholds, run tests, and generate text and html reports.