Testing in NestJS

Hold up, so why unit test?

Just a few reasons (of many)...

• Find bugs early
• Find regressions before someone else finds them
• Supports easier implementation refactoring
• Pseudo documentation in code
• etc...

Tests must be part of Continuous Integration processes as well as able to run on a local developer's machine

Testing in NestJS

• Uses Jest, by default, as test runner and assertion library
  • see https://jestjs.io/docs/en/getting-started
• Uses supertest for test web client (e2e tests)
  • see https://github.com/visionmedia/supertest

What to test?

• Database interactions
• API endpoints (end-to-end)
• ...
• ...
• Basically everything...

80% code coverage is required for this contract

Tactical testing principles

• Avoid having side effects in your functions! (eg. avoid global state)
• Tests should NOT rely on testing order (run independently)
• Tests should be repeatable
• Fuzzing your inputs

Simple Example

see https://gitlab.com/meilinger/nestjs-testing

Resources

• https://nestjs.com/
• https://jestjs.io/
• https://github.com/visionmedia/supertest
• https://hackernoon.com/introduction-to-test-driven-development-tdd-61a13bc92d92

Exercises

• https://sites.google.com/site/tddproblems/all-problems-1
• https://medium.com/@marlenac/learning-tdd-with-katas-3f499cb9c492