Tests in projects help us create stable applications and we should do them as a part of any project. While there are different kinds of tests, we mostly write unit and integration tests in .NET development. Tests are always written in a separate project. We use xUnit testing tool by default, along with Moq for mocking and Fluent Assertions for building assertion rules. The tests are structured using the Arrange-Act-Assert pattern which helps us write readable and understandable code.