Part 4 — Testing the Backend: Jest, Supertest, and Auth Guards

Before you write your first test, you need a stable foundation: Jest configuration, test modules, a sandboxed PostgreSQL database, and a clean Prisma workflow for reproducible tests.

In this post, you’ll learn how to isolate and test NestJS services, validate DTOs programmatically, and verify custom pipes with clear testing strategies.

Integration tests verify the entire request pipeline—controllers, DTOs, pipes, filters, interceptors, and database behavior. This post shows how to test your REST API like a professional.

Authentication logic is critical—and fragile if untested. In this post, you’ll learn how to test JWT auth guards and protected REST routes with confidence.

Reliable backend tests require strict database isolation and disciplined CI workflows. This post shows how to reset PostgreSQL safely, use transactions, and run tests confidently in automation.

Writing tests is easy. Maintaining hundreds of them is hard. This post shows how to structure your NestJS backend tests so they scale without pain.