06/04/2021

Unit tests

Unit tests are tests of modularity
They test specific part/piece of the system (called module) independently from other modules of the system
For example, test of module (component in Front End) that shows red error text:
- module has input data (error status - existing or not)
- output data" is
  - null (if error does not exist)
  - red text (if error exists)
- unit test should check that module/component returns specific output data based on input data
- in the system this module get input data (error status) from other module
  - we don’t care about that because unit test checks module independently from other modules
- for checking interaction between several modules we should use Integration tests
Unit tests are documenting behavior of specific module

Basically, it’s module
- In languages like JavaScript modules are mostly files
  - But if file contains few classes then
    - classes are modules
    - file isn’t module
An example in React development
- React app consists of components
- Each component could contain:
  - state
  - methods (in class component) or functions (in functional component)
- It doesn’t make sense to test each function/method of the component because:
  - a function/method doesn’t make sense outside of the component
  - a function/method most likely updates component’s state
- A unit here is the component itself
Unit is a stateless function
- It could be classic helper function