Testing Strategies for TypeScript APIs That Actually Catch Bugs

Testing Strategies for TypeScript APIs That Actually Catch Bugs Most API test suites are theater. They test that 200 OK is returned for valid input, but miss the edge cases that break production — race conditions, partial failures, invalid state transitions, and subtle serialization bugs. Here's a testing strategy built from real production incidents, organized by what each test type catches and how much it costs to maintain. The Testing Pyramid for APIs / E2E \ — 5% of tests, catch integration failures / Contract \ — 15%, catch API compatibility breaks / Integration \ — 30%, catch database + service bugs / Unit Tests \ — 50%, catch logic bugs fast Project Setup mkdir api-testing && cd api-testing npm init -y npm install express zod drizzle-orm better-sqlite3 npm install -D vitest supertest @types/supertest testcontainers msw // vitest.config.ts import { defineConfig } from ' vitest/config ' ; export default defineConfig ({ test : { globals : true , environment : ' node ' , coverage :