Jest LESSONS.md

Lessons Learned while Learning Jest

1. Don't expect to use only Jest. Jest struggles with certain things and it is just more effective to use something like Cypress or Selenium.
2. A common React pattern seems to be you only test the current component and mock all the children.
3. Mocking native browser objects can be accomplished by importing a module that defines objects in the global space using Object.defineProperty.
   • Warning: This really only works for a SINGLE PROPERTY. If you are mocking an entire class (like MediaRecorder) then you will need to mock the entire class with your own custom class.
4. The Jest documentation doesn't really work for me. I can't put my finger on it but I often find myself wondering what the recommended best practices are.
5. (already knew this but have a prime example) Don't test native objects. In my case, I've been working with MediaRecorder. There is no need to test the .start method. It will work. Likewise, there is no need to test whether or not calling start also calls the onstart event handler (it will). Therefore, if you have code that you want to test in the onstart event handler, you should define it in a separate function and test that function.
6. There is no uncomplicated way to test the code inside the native event handlers of MediaRecorder because MediaRecorder is mocked.