Unit Testing

Question 1

What is unit testing?

Answer 1

Unit testing is a software testing technique where individual components or units of a program are tested in isolation to ensure they work as expected.

Question 2

Why is unit testing important?

Answer 2

Unit testing helps identify defects early in the development cycle, ensures code quality, facilitates code maintenance, and provides documentation for how code is expected to work.

Question 3

What is a unit test case?

Answer 3

A unit test case is a set of conditions, inputs, and expected outputs designed to verify the behavior of a specific unit (such as a function or method) of code.

Question 4

What is mocking in unit testing?

Answer 4

Mocking is a technique used to create simulated versions of dependencies that a unit being tested relies on. This allows isolating the unit under test and controlling the behavior of its dependencies.

Question 5

What is a mocking framework?

Answer 5

A mocking framework is a tool or library that simplifies the process of creating mock objects for unit testing.

Question 6

Name some popular mocking frameworks for .NET.

Answer 6

Moq, Rhino Mocks, NSubstitute, FakeItEasy.

Question 7

Explain the Arrange-Act-Assert pattern in unit testing.

Answer 7

Arrange: Set up the test environment, including creating mock objects and arranging inputs.

Act: Perform the action being tested.

Assert: Verify the expected outcomes by checking the results against expected values.

Question 8

What is a mock object?

Answer 8

A mock object is a simulated object used in unit testing to replace real dependencies. It allows controlling the behavior of these dependencies during testing.

Question 9

How does Moq work?

Answer 9

Moq is a mocking framework for .NET. It dynamically generates mock objects based on interfaces or classes, allowing you to set up expectations and behavior for these mocks.

Question 10

What is a stub? How is it different from a mock?

Answer 10

A stub is a simplified implementation of an interface or class that returns pre-defined values. It doesn’t contain behavior verification like a mock. Stubs are used when you only need to provide certain responses from dependencies.

Question 11

What is dependency injection?

Answer 11

Dependency injection is a design pattern that involves passing dependencies (such as services, repositories) into a class rather than having the class create its own dependencies. This promotes better separation of concerns and testability.

Question 12

How does dependency injection help with unit testing?

Answer 12

Dependency injection allows you to inject mock objects or stubs in place of real dependencies, making it easier to isolate units for testing.

Question 13

Explain the difference between mocking and stubbing.

Answer 13

Mocking involves creating objects that simulate real behavior, including verifying interactions between objects.

Stubbing involves creating objects that provide pre-defined responses to method calls, without verifying interactions.

Question 14

What is the purpose of using the “Verify” method in a mocking framework?

Answer 14

The “Verify” method in a mocking framework is used to assert that a specific method of a mock object was called with the expected parameters during the test.

Question 15

How do you handle complex scenarios when multiple dependencies are involved in unit testing?

Answer 15

You can use the mocking framework to set up expectations and behaviors for each dependency. You might need to create multiple mock objects and configure them accordingly.

Question 16

What are some common mistakes to avoid when writing unit tests?

Answer 16

Testing implementation details, overly complex test cases, not testing edge cases, not cleaning up after tests (e.g., leaving mock state unchanged).

Question 17

What is a code coverage metric, and how is it relevant to unit testing?

Answer 17

Code coverage measures the proportion of your codebase that is executed during testing. It helps identify areas that aren’t adequately covered by tests, guiding additional testing efforts.

Question 18

How can you ensure that your unit tests remain maintainable as your codebase evolves?

Answer 18

Follow the SOLID principles, write tests that focus on behavior rather than implementation, and refactor tests as your code changes to keep them aligned with your code’s behavior.

Question 19

What are parameterized tests? How can they be useful in unit testing?

Answer 19

Parameterized tests allow you to run the same test logic with different inputs and expected outcomes. They can be useful for testing a method’s behavior across various scenarios.

Question 20

Explain the concept of “test doubles.”

Answer 20

Test doubles are objects used in unit testing to replace real dependencies, including stubs, mocks, fakes, and dummies.

Question 21

When should you use a stub instead of a mock in unit testing?

Answer 21

Use a stub when you only need to provide specific responses from a dependency without verifying how that dependency was used.

Question 22

What is a “test pyramid,” and how does it relate to unit testing?

Answer 22

The test pyramid is a metaphorical representation of the ideal distribution of tests in a software application: more unit tests at the base, fewer integration tests in the middle, and even fewer end-to-end tests at the top.

Question 23

How can you write unit tests for code that interacts with external resources like databases or web services?

Answer 23

Use techniques like dependency injection and mocking to isolate the code from external resources. You can mock database or service calls to ensure consistent test behavior.

Question 24

What is a “test harness”?

Answer 24

A test harness is a set of tools, scripts, or frameworks used to automate the process of running tests and collecting test results.

Question 25

Explain the concept of “test-driven development” (TDD).

Answer 25

Test-driven development involves writing tests before writing the actual code. Tests drive the development process and help ensure that code meets the specified requirements.

Question 26

What is a “test fixture”?

Answer 26

A test fixture is a defined state or environment in which a set of tests are executed. It includes the setup and cleanup necessary to ensure consistent test conditions.

Question 27

Why should you avoid using Thread.Sleep in unit tests?

Answer 27

Thread.Sleep introduces unnecessary delays in test execution, making tests slower and less reliable. Instead, consider using mock objects or other techniques to control timing.

Question 28

How can you handle static methods or properties in unit testing, considering they can’t be easily mocked?

Answer 28

Refactor the code to make static methods more testable. One approach is to wrap static method calls in instance methods of a new class, which can then be mocked.

Question 29

What is “behavior verification” in unit testing?

Answer 29

Behavior verification involves checking whether a method or function on a mock object was called with specific parameters during the test.

Question 30

Explain the concept of “test isolation.”

Answer 30

Test isolation refers to the practice of running each test in isolation from others, ensuring that one test’s outcome doesn’t affect another test.

Question 31

When might you choose to use a “partial mock”?

Answer 31

A partial mock is used when you want to mock only specific methods of a class while using the real implementation for others.

Question 32

What are some challenges you might face when mocking external dependencies in unit tests?

Answer 32

Changes in the external dependency’s interface, maintaining mock behavior when the dependency changes, handling complex scenarios in the dependency’s behavior.

Question 33

What is the purpose of using a “fake” in unit testing?

Answer 33

A fake is a simplified implementation of a dependency that is used to replace the real implementation in tests. Fakes are often used for performance reasons.

Question 34

What is “mock state verification”?

Answer 34

Mock state verification involves checking the state of a mock object after a test to ensure it was used as expected during the test.

Question 35

How do you deal with time-dependent code in unit tests?

Answer 35

You can use techniques like dependency injection to provide a controllable time source. For example, you can inject a “time provider” that returns a fixed time value during tests.

Question 36

What is “test smell,” and how can you identify it in your unit tests?

Answer 36

Test smells are indicators of poor test design or maintenance. They can include overly complex setups, duplicated code, tight coupling between tests and implementation, and lack of readability.

Question 37

Explain the concept of “test suite” in unit testing.

Answer 37

A test suite is a collection of test cases that are grouped together to be executed as a single unit. Test suites can be organized based on different criteria, such as functionality or module.

Question 38

What is a “test runner,” and how does it relate to unit testing?

Answer 38

A test runner is a tool or framework that discovers and executes your unit tests. It provides the necessary environment for running tests and reports the test results

Question 39

How do you handle exceptions in unit tests, especially when dealing with mock objects?

Answer 39

Configure your mock objects to throw exceptions as needed to simulate different scenarios. Use assertions to verify that the expected exceptions are caught and handled appropriately.

Question 40

What is “test coverage,” and why is it important in unit testing?

Answer 40

Test coverage measures the extent to which your code is exercised by tests. It helps identify areas of the code that aren’t adequately tested, guiding additional testing efforts.

Question 41

How can you ensure that your unit tests are not too fragile?

Answer 41

Avoid testing implementation details, use parameterized tests, focus on testing behavior, and write tests that are resistant to changes in the codebase.

Question 42

Explain the term “test double” and provide examples of different types of test doubles.

Answer 42

A test double is a generic term for any object used in tests as a substitute for a real dependency. Examples include stubs, mocks, fakes, and dummies.

Question 43

What are some potential disadvantages of relying heavily on mocking in unit tests?

Answer 43

Overuse of mocking can lead to tests that are tightly coupled to the implementation, making refactoring difficult. It can also result in tests that don’t accurately reflect real-world behavior.

Question 44

How can you ensure that your unit tests are readable and maintainable by other team members?

Answer 44

Follow consistent naming conventions, provide clear and concise comments, and structure tests using the Arrange-Act-Assert pattern.

Question 45

When might you choose to use a “spy” in unit testing?

Answer 45

A spy is used to track calls made to a real object while still allowing the real implementation to execute. This can be useful when you want to verify interactions while retaining real behavior.

Question 46

What is “test stability,” and how can you improve it in your unit tests?

Answer 46

Test stability refers to the reliability of tests in producing consistent and accurate results. You can improve test stability by reducing flakiness, using deterministic data, and avoiding Thread.Sleep.

Question 47

What is “test coverage gap,” and how can you identify and address it in unit testing?

Answer 47

A test coverage gap is an area of code that isn’t adequately covered by tests. You can identify it through code coverage analysis and address it by creating additional test cases.

Question 48

How do you handle external dependencies that are difficult to mock, such as third-party libraries or framework classes?

Answer 48

Create wrapper classes or interfaces around the external dependencies, and then use dependency injection to inject these wrappers into your code. This way, you can easily mock the wrappers in your tests.

Question 49

What is “test context” in unit testing, and why is it important?

Answer 49

The test context includes all the relevant conditions, dependencies, and data that surround a particular test case. Properly setting up the test context is crucial for ensuring accurate and isolated testing.