What is a mock in testing and why is it needed?

Mock in tests is a stub object that simulates the behavior of a real component or module with which the tested code interacts. It is used to isolate the tested code from external dependencies to verify the logic without influence from real external factors (such as databases, network requests, file systems).

Example: if a function calls an external service, instead of making a real call, we use a mock that returns a pre-defined result. This allows tests to be fast, reliable, and reproducible.

In C++, libraries like Google Mock are often used to create mock objects, which allow setting expectations for calls and return values.