Read Apple’s swift-testing documentation.

Read Hello Swift Testing, Goodbye XCTest.

Read iOS Unit Test Master 101 — Vol. 1. Learned new terms. “Test Doubles”: test objects that are used to mimic the behavior of some real object. I always called this mocks. But no. Test double could be a “Dummy”, “Fake”, “Stub”, “Spy” or “Mock”. “Fixture”: predefined set of conditions or data used to initialize a system or environment for testing, ensuring consistent and repeatable results. I knew what is that. But use case example is very good.