Where in tests is the behavior logic of objects implemented?

The behavior logic of objects in tests is usually implemented using mocks or stubs. These are special objects that imitate the behavior of real dependencies, allowing control over their responses and verification of interactions.

In C#, libraries like Moq are often used for this purpose. In tests, mock objects are created, their behavior is configured (for example, what a method should return), and it is checked that the tested object interacts with them correctly.

Example with Moq:

var mockRepository = new Mock<IRepository>();
mockRepository.Setup(r => r.GetData()).Returns("Test data");

var service = new MyService(mockRepository.Object);
var result = service.ProcessData();

mockRepository.Verify(r => r.GetData(), Times.Once);
Assert.AreEqual("Processed: Test data", result);

Thus, the behavior logic of objects in tests is implemented through configuring and verifying the behavior of mock objects, rather than through real implementations.