1. What is Integration Testing?

Integration testing is a type of software testing where individual units or components are combined and tested as a group. Its purpose is to detect errors in the interaction between integrated units.

Example: Verifying how the login module interacts with the database module.

2. Why is Integration Testing important?

It ensures that different components of an application work together seamlessly, preventing major issues in production.

Key benefits:

• Identifies interface defects early.
• Improves system reliability.
• Reduces debugging time.

3. What are the different types of Integration Testing?

• Big Bang Integration: Testing all components together at once.
• Top-Down Integration: Testing from top-level modules to sub-modules.
• Bottom-Up Integration: Testing from sub-modules to the top-level modules.
• Sandwich (Hybrid) Integration: Combines top-down and bottom-up approaches.

4. Explain the Big Bang Integration approach.

In this approach, all components are integrated and tested simultaneously. While it saves time during preparation, it can be difficult to isolate issues.

5. What are the challenges of Integration Testing?

• Complexity in managing dependencies.
• Time-consuming test case creation.
• Identifying the root cause of issues in interfaces.

6. What is the difference between Integration Testing and Unit Testing?

• Unit Testing: Tests individual components in isolation.
• Integration Testing: Tests the interaction between multiple components.

7. What tools are commonly used for Integration Testing?

• Jenkins: For Continuous Integration.
• JUnit/TestNG: For Java applications.
• Postman: For API testing.
• Selenium: For UI testing.
• SoapUI: For web services.

8. What is a Stubs and Drivers in Integration Testing?

• Stub: Simulates lower-level modules.
• Driver: Simulates higher-level modules.

These are used in top-down and bottom-up integration testing, respectively.

9. When should Integration Testing be performed?

It is performed after unit testing and before system testing during the software development lifecycle.

10. How do you decide test cases for Integration Testing?

Test cases should focus on:

• Data flow between modules.
• Interfaces and APIs.
• Error handling in communication.

11. What is the purpose of an Integration Test Plan?

It outlines:

• Objectives of testing.
• Scope and coverage.
• Roles and responsibilities.
• Test environment setup.
• Deliverables.

12. Explain Top-Down Integration Testing.

Testing starts with high-level modules, integrating and testing lower-level modules step by step using stubs for missing modules.

13. Explain Bottom-Up Integration Testing.

Testing begins with low-level modules, progressively integrating higher-level modules using drivers.

14. What is the role of Mock Objects in Integration Testing?

Mock objects simulate the behavior of real modules to test components independently.

15. How does Continuous Integration relate to Integration Testing?

Continuous Integration automates the integration and testing process, ensuring that all changes integrate without issues.

16. What is System Integration Testing (SIT)?

SIT tests the interaction between different systems, verifying data flow and interoperability.

17. How do you test APIs in Integration Testing?

• Use tools like Postman or SoapUI.
• Validate request-response cycles.
• Check error codes and data consistency.

18. What are key metrics in Integration Testing?

• Number of defects found.
• Test coverage.
• Time to test.
• Pass/fail rates.

19. Describe Hybrid Integration Testing.

A combination of top-down and bottom-up integration testing, leveraging the advantages of both methods.

20. What is a Test Harness in Integration Testing?

A test harness includes stubs, drivers, and scripts used to simulate environments for testing integrated components.

21. How do you ensure coverage in Integration Testing?

By using:

• Functional specifications.
• Interface design documents.
• Dependency diagrams.

22. What is the difference between Smoke Testing and Integration Testing?

• Smoke Testing: Verifies basic functionality.
• Integration Testing: Focuses on interactions between components.

23. What is Incremental Integration Testing?

A systematic approach to integrating and testing components in a sequence, either top-down or bottom-up.

24. How do you handle integration issues?

• Analyze logs and trace errors.
• Isolate problematic modules.
• Fix interface and dependency mismatches.

25. How do you mock third-party APIs during testing?

• Use tools like WireMock or MockServer.
• Simulate API responses to ensure consistent testing.

26. What is Parallel Integration Testing?

Testing multiple modules simultaneously to reduce time but requires robust test planning.

27. How do you validate database interactions in Integration Testing?

• Check SQL query executions.
• Verify data consistency.
• Test database triggers and constraints.

28. What is the difference between Integration Testing and System Testing?

• Integration Testing: Tests interactions between modules.
• System Testing: Tests the application as a whole.

29. What is the role of a Test Environment in Integration Testing?

A test environment replicates the production setup to test real-world interactions.

30. How do you document Integration Testing results?

Include:

• Test scenarios and cases executed.
• Observations and defects.
• Test logs and screenshots.

These questions and answers provide an in-depth understanding of integration testing, ensuring that candidates are well-prepared for interviews.