JavaScript Mocking Fundamentals

TestingJavaScript.com

Learn how mocking in JavaScript tests works by implementing them from scratch!

In this material, we have a set of no-framework tests that correspond to a set of jest tests (in the __tests__ directory). The idea is that (with the exception of the first test), you look at the jest version first, then see how that would be implemented without a testing framework.

Order of material:

1. monkey-patching.js (no jest version)
2. mock-fn.js
3. spy.js
4. inline-module-mock.js
5. external-mock-module.js

The files are intended to test the thumb-war.js module and mock the utils module.

To run the tests, run npx jest. To start watch mode run npx jest --watch

Custom jest runner.

You can definitely run the no-framework files just using node (like this: node src/no-framework/monkey-patching.js), but in an effort to make running these easier, I created a custom jest runner that uses jest to run the files, but allow them to be run without the jest testing framework. It's really cool. It uses create-jest-runner and should probably be published eventually.