Tests are pieces of code that test other pieces of code or functionality of an app.
We can divide tests into four general groups:
Unit test: In this test, we test only a small unit of our code. This can, for example, be a function or a piece of code. Unit tests should not call other functions, write to the hard disk or database, or access the network. If such functionality is needed, one should write stubs, which are functions that return the expected value without calling the real function.
Integrations test: In this test, we combine multiple tests and run them in different environments to make sure that they still work. The difference in this test compared to the unit test is that we are actually running connected functionalities, such as calling the database.
Functional test: This can be a unit test or tests in the interface, but will only test the functionality of a feature/function without checking for side effects, such as whether or not variables were cleaned up properly...