You can have many types of tests. First you have assertions and unit tests with mocks/injections that runs at compile time together with the type checker and ot

You can have many types of tests. First you have assertions and unit tests with mocks/injections that runs at compile time together with the type checker and other low level tests. Then you have the integration tests that makes sure your code works together with third parties and other API's. Those tests might seem unnecessary when you already have unit tests, but it's very nice to know if some third party have made breaking changes and that your software have stopped working because of it.