What is the difference between mock objects and stubs in testing?

In testing, mocks and stubs serve as replacements for real components but have different purposes:

• Stub — a simple object that returns predefined data so that the test can operate with predictable behavior. It does not check how it is called, just provides the necessary responses.

• Mock — an object that not only mimics behavior but also verifies that methods were called with expected parameters and in the correct order. Mocks are used to verify interactions.

Example:

• A stub might return a fake response from a network request.
• A mock will check that the request method was called exactly once with a specific URL.

In iOS, frameworks like OCMock or Cuckoo are often used to create mocks and stubs.