What is mocking?
💡 Concept: Mocking in Unit Testing
Mocking is a technique to create fake objects that simulate behavior of real dependencies for unit testing.
📘 Quick Intro
Mocks help isolate the unit under test by providing controlled behavior and verifying interactions.
🧠 Analogy
Like using stunt doubles in movies to test scenes without risking the main actor.
🔧 Technical Explanation
- Mocks implement interfaces or abstract classes.
- Provide predefined responses for method calls.
- Can verify if methods were called or not.
- Common mocking frameworks: Moq, NSubstitute, FakeItEasy.
- Enhances test reliability and speed.
🎯 Use Cases
- ✅ Simulating database or web service calls.
- ✅ Testing error conditions.
- ✅ Verifying interactions between components.
- ✅ Isolating units from external dependencies.
💻 Code Example
// Using Moq for mocking
var mockRepo = new Mock();
mockRepo.Setup(repo => repo.GetUser(It.IsAny<int>())).Returns(new User { Id = 1, Name = "Test" });
var service = new UserService(mockRepo.Object);
var user = service.GetUser(1);
mockRepo.Verify(repo => repo.GetUser(1), Times.Once);
❓ Interview Q&A
Q1: What is mocking?
A: Creating fake objects for unit tests.
Q2: Why use mocking?
A: To isolate the unit under test.
Q3: Name some mocking frameworks.
A: Moq, NSubstitute, FakeItEasy.
Q4: Can mocks verify method calls?
A: Yes.
Q5: What is the difference between mocks and stubs?
A: Mocks verify behavior; stubs provide data.
Q6: Can you mock concrete classes?
A: Sometimes, depending on framework.
Q7: Is mocking only for unit testing?
A: Primarily, yes.
Q8: What is a test double?
A: General term for fake test objects.
Q9: Does mocking slow tests?
A: Usually no, it speeds them up.
Q10: Can mocking detect unwanted calls?
A: Yes, through verification.
📝 MCQs
Q1. What is mocking?
- Creating fake objects
- Calling real methods
- Using database
- Integration testing
Q2. Why use mocking?
- To slow tests
- To isolate the unit
- To mock UI
- For production
Q3. Name a mocking framework.
- NUnit
- Moq
- XUnit
- Selenium
Q4. Can mocks verify calls?
- No
- Yes
- Sometimes
- Never
Q5. Mocks vs stubs?
- Mocks provide data
- Mocks verify behavior
- Stubs verify behavior
- No difference
Q6. Can you mock concrete classes?
- Always
- Sometimes
- Never
- Rarely
Q7. Is mocking only for unit tests?
- No
- Yes
- Sometimes
- Rarely
Q8. What is a test double?
- Real object
- Fake test object
- Database
- UI
Q9. Does mocking slow tests?
- Yes
- No
- Sometimes
- Rarely
Q10. Can mocking detect unwanted calls?
- No
- Yes
- Maybe
- Never
💡 Bonus Insight
Mocking improves test isolation and reliability by simulating dependencies in unit tests.
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