API Testing Interview
Questions & Answers
1. What is API testing, and why is it important in software development?
• API testing is the process of testing application programming interfaces (APIs) to ensure
they meet functional, performance, security, and reliability requirements.
• APIs allow different software systems to communicate and exchange data.
• API testing is crucial in software development because it verifies the correct behavior,
functionality, and integration of APIs, ensuring they work as intended and enable
seamless interaction between different components of an application or between
different applications.
2. Explain the main differences between UI testing and API testing?
UI Testing API Testing
User interface of an
Focus Functionality and behavior of APIs
application
Involves interacting with
Interaction Directly calls API endpoints and verifies responses
graphical elements.
Concerns User experience Data validation, integration, security, and performance
Verifies the application's
Scope Validates the API's responses and data
visual appearance
Dependent on the UI and
Dependencies Independent of UI components
its components
Usually performed at the
Testing Level end of the development Performed at the integration and system level
cycle
Automation tools like
Tools API testing tools like Postman, RestAssured, etc.
Selenium, Appium, etc.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
3. What are the key elements you consider when designing an API test suite?
When designing an API test suite, the key elements to consider include:
✓ Identifying the APIs to be tested and their specific endpoints.
✓ Determining the required test data and input parameters for each API endpoint.
✓ Defining the expected outcomes or responses for each API request.
✓ Ensuring proper test coverage by considering various scenarios, error conditions, and
edge cases.
✓ Incorporating test environment setup and teardown processes.
✓ Determining the necessary authentication or authorization mechanisms for testing the
APIs.
✓ Considering performance testing, security testing, and error handling within the test
suite.
4. How do you ensure API test coverage? What techniques or tools do you use?
To ensure API test coverage, the following techniques and tools can be used:
✓ Analyzing the API documentation to identify all available endpoints and methods.
✓ Utilizing code coverage analysis tools to measure the extent of code coverage achieved
by the tests.
✓ Employing test case management tools to track and manage the test coverage.
✓ Employing equivalence partitioning and boundary value analysis techniques to cover
different input ranges and edge cases.
✓ Utilizing exploratory testing techniques to uncover unforeseen scenarios.
✓ Employing contract testing to ensure compatibility between API consumers and
providers.
✓ Utilizing tools that generate code snippets for various programming languages to
automate the creation of test cases.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
5. What are some common challenges you've encountered while testing APIs, and how
did you overcome them?
Some common challenges encountered while testing APIs include:
✓ API availability and stability issues: To overcome this, thorough monitoring and
communication with the API providers is essential. Implementing retry mechanisms,
handling timeouts, and designing test cases to handle intermittent failures can also help.
✓ Lack of proper documentation: When faced with incomplete or inaccurate
documentation, reaching out to developers or API providers for clarification is important.
Utilizing tools like API explorers or reverse engineering techniques can also aid in
understanding API behavior.
✓ Test data management: Efficiently managing test data can be a challenge. Using tools
to generate test data or leveraging mock servers can help overcome this challenge.
✓ Authentication and authorization complexities: Properly understanding and
implementing authentication and authorization mechanisms are crucial. Collaborating
with security experts and utilizing tools for managing authentication tokens can aid in
overcoming these challenges.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
6. Describe the process you follow when testing an API endpoint for the first time.
When testing an API endpoint for the first time, the following process can be followed:
✓ Understand the API documentation, including the purpose, functionality, input
parameters, and expected responses of the API endpoint.
✓ Set up the necessary test environment, including any required dependencies or mock
servers.
✓ Design test cases to cover different scenarios, including positive and negative test
cases, boundary values, and error conditions.
✓ Construct the API request based on the endpoint and required input parameters.
✓ Execute the API request and capture the response.
✓ Validate the response against the expected outcomes, ensuring data correctness,
appropriate status codes, and error handling.
✓ Repeat the process with different inputs, scenarios, and edge cases to achieve
comprehensive test coverage.
✓ Log any issues or defects encountered during the testing process, providing detailed
information for debugging and resolution.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
7. How do you handle authentication and authorization in API testing?
Authentication and authorization in API testing can be handled by:
✓ Understanding the authentication mechanisms supported by the API, such as API keys,
OAuth, JWT, or session-based authentication.
✓ Configuring the test environment with the necessary authentication credentials or
tokens.
✓ Incorporating authentication parameters into API requests, such as headers or tokens, to
authenticate the test requests.
✓ Verifying that the API responses include the expected authorization status codes or error
messages for unauthorized requests.
✓ Testing different scenarios, including valid and invalid credentials, to ensure proper
authentication and authorization behavior.
8. What types of security testing do you perform on APIs?
Security testing on APIs typically includes:
✓ Input validation: Ensuring that the API validates and sanitizes input data properly to
prevent injection attacks.
✓ Authentication and authorization testing: Verifying that the authentication and
authorization mechanisms function correctly and that unauthorized access is restricted.
✓ Session management: Testing the session management techniques, such as token
expiration and revocation, to prevent unauthorized access to user sessions.
✓ Data protection: Ensuring that sensitive data transmitted through the API is properly
encrypted using secure protocols.
✓ Error handling and logging: Checking that error messages and logging practices do not
expose sensitive information.
✓ API rate limiting: Testing the API's rate limiting functionality to prevent abuse and ensure
fair usage.
✓ Penetration testing: Performing simulated attacks to identify vulnerabilities and
weaknesses in the API's security measures.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
9. What is the role of mock servers in API testing, and how do you utilize them?
✓ Mock servers play a significant role in API testing by simulating the behavior of the
actual API endpoints. They allow testing to be performed without relying on the real API
infrastructure, enabling faster and isolated testing. Mock servers can be utilized in the
following ways:
✓ Creating simulated API responses for different scenarios to test various inputs and edge
cases.
✓ Replicating error conditions or response codes to validate error handling and resilience
of the client application.
✓ Facilitating parallel development and testing by decoupling the development of the client
application from the availability of the real API.
✓ Enabling continuous integration and delivery processes by providing reliable and
consistent responses during automated testing.
✓ Supporting the testing of APIs that are still under development or not yet available.
✓ Facilitating API contract testing by defining the expected behavior of the API endpoints
without relying on the real implementation.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
10. How do you handle testing scenarios that involve asynchronous API calls?
When testing scenarios that involve asynchronous API calls, the following steps can be
followed:
✓ Understand the asynchronous nature of the API calls and the expected behavior in
terms of responses and callbacks.
✓ Design test cases to cover different stages of the asynchronous process, such as
initiating the request, polling for status updates, and handling callbacks.
✓ Implement proper synchronization mechanisms to wait for the expected responses or
events during testing.
✓ Utilize tools or libraries that support asynchronous testing to handle complex scenarios
effectively.
✓ Verify that the API responses and callbacks are received within the expected time frame.
✓ Consider edge cases, such as timeouts or errors during asynchronous processing, and
test the error handling and fallback mechanisms accordingly.
11. How do you handle data validation in API testing? What techniques or tools do you
use?
Data validation in API testing can be handled using the following techniques and tools:
✓ Use assertions or validations in your test framework to compare the API response data
with expected values or patterns.
✓ Leverage schema validation tools like JSON Schema or XML Schema to ensure the
response structure conforms to the expected format.
✓ Verify the correctness of specific data fields or properties by comparing them against
known values or ranges.
✓ Utilize regular expressions or pattern matching libraries to validate the format of specific
data fields, such as email addresses or phone numbers.
✓ Validate the consistency and integrity of data returned from different API endpoints by
cross-referencing related data.
✓ Implement custom validation functions or scripts to perform complex data validations
based on specific business rules or requirements.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
12. What are some common performance testing techniques for APIs, and how do you
measure API performance?
Common performance testing techniques for APIs include:
✓ Load testing: Simulating concurrent requests from multiple users to assess the API's
performance under expected or anticipated load conditions.
✓ Stress testing: Pushing the API to its limits by generating a high volume of requests to
identify its breaking point or performance bottlenecks.
✓ Endurance testing: Evaluating the API's performance over an extended period,
monitoring for memory leaks or resource exhaustion.
✓ Spike testing: Simulating sudden spikes in the number of requests to determine how the
API handles sudden bursts of traffic.
✓ Latency testing: Measuring the response time or latency of the API under normal and
peak load conditions to ensure it meets performance requirements.
✓ Utilizing performance testing tools like Apache JMeter, Gatling, or Locust to simulate
different load scenarios and measure response times, throughput, and resource
utilization.
✓ Monitoring network traffic, CPU usage, memory consumption, and other system metrics
to identify performance issues and bottlenecks.
13. What is the role of API documentation in API testing, and how do you utilize it?
✓ API documentation plays a crucial role in API testing by providing information about the
API's endpoints, parameters, expected responses, error codes, and authentication
mechanisms. It serves as a reference guide for testing and aids in understanding the
API's functionality. To utilize API documentation effectively in API testing:
✓ Study the documentation thoroughly to gain a clear understanding of the API's
capabilities and expected behaviors.
✓ Use the documentation as a reference to design test cases and ensure appropriate
coverage of all endpoints and functionalities.
✓ Verify the accuracy and consistency of the API's behavior against the documented
specifications.
✓ Refer to the documentation to identify and utilize any required authentication tokens,
headers, or parameters during API testing.
✓ Collaborate with developers or API providers to clarify any ambiguities or inconsistencies
in the documentation.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
14. Can you explain the concept of contract testing and its importance in API testing?
Contract testing is a technique in API testing that focuses on ensuring compatibility and
agreement between the provider and consumer of an API. It involves creating and verifying
contracts that specify the expected behavior of API endpoints. The contracts define the
expected requests, responses, and data formats, acting as a shared agreement between the
API provider and consumer. The importance of contract testing in API testing includes:
Ensuring that both the API provider and consumer are in sync regarding the expected API
behavior.
✓ Preventing compatibility issues between different versions or implementations of an API.
✓ Facilitating independent development and testing of the API provider and consumer.
✓ Reducing dependencies on real API endpoints during testing by using contract stubs or
mocks.
✓ Enhancing collaboration and communication between teams by providing a clear
understanding of API expectations.
15. How do you handle versioning and backward compatibility in API testing?
✓ Handling versioning and backward compatibility in API testing involves the following
practices:
✓ Incorporating versioning in the API endpoints or request headers to support different API
versions.
✓ Creating test cases that cover both the current and previous versions of the API to
ensure backward compatibility.
✓ Verifying those changes in newer API versions do not break existing consumer
applications.
✓ Using contract testing to establish and maintain compatibility between the API provider
and consumer.
✓ Designing test cases that specifically target backward compatibility scenarios and edge
cases.
✓ Collaborating with API providers and consumers to align versioning strategies and
ensure smooth transitions between API versions.
✓ Documenting changes between API versions and communicating them effectively to all
stakeholders.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
16. Describe a scenario where you had to debug an API-related issue. What steps did you
take to identify and resolve the problem?
Scenario:
During testing, an API consistently returned an error response with an unclear error
message, making it challenging to identify the root cause:
Steps taken to identify and resolve the problem:
✓ Analyzed the error response: Examined the error response in detail, looking for any
clues, error codes, or specific error messages.
✓ Checked the API documentation: Cross-referenced the error codes or messages
received with the API documentation to gain a better understanding of their meanings
and possible causes.
✓ Reviewed the API request and parameters: Verified the correctness of the API
request, including the headers, query parameters, or payload, to ensure they matched
the expected format and values.
✓ Inspected the server logs: Examined the server logs to identify any error messages,
stack traces, or exceptions related to the API request, focusing on any relevant
timestamps or error codes.
✓ Reproduced the issue in a controlled environment: Tried to reproduce the error
scenario in a controlled test environment, making adjustments to the request parameters
or test setup as necessary.
✓ Collaborated with developers: Engaged with the API developers to discuss the issue,
provide them with detailed information, and seek their assistance in identifying the
problem.
✓ Applied debugging techniques: Leveraged debugging tools or techniques to step
through the code and track the flow of execution, observing variables and checking for
any unexpected behavior or exceptions.
✓ Implemented logging and additional checks: Added logging statements or additional
checks within the code to gather more information about the execution flow and data
state.
✓ Tested alternative scenarios: Explored alternative scenarios or corner cases that could
shed light on the issue or reveal related problems.
✓ Implemented a fix or workaround: Once the issue was identified, worked with the
development team to implement a fix or a workaround, and retested to ensure the
problem was resolved.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
17. What are some best practices for designing and maintaining API test cases?
Some best practices for designing and maintaining API test cases include:
✓ Test case modularity: Design test cases that are modular and reusable, focusing on
specific API functionalities or endpoints.
✓ Test case independence: Ensure test cases can be executed independently of each
other to avoid dependencies and allow for easier test maintenance.
✓ Test case data separation: Separate test data from test case logic, using external files
or databases to manage test data.
✓ Test case prioritization: Prioritize test cases based on risk, criticality, or impact, and
execute them accordingly.
✓ Test case parameterization: Parameterize test cases to cover different scenarios and
variations using data-driven techniques.
✓ Test case documentation: Clearly document test case purpose, expected outcomes,
preconditions, and postconditions for easy understanding and future maintenance.
✓ Test case versioning: Maintain version control for test cases to track changes,
enhancements, and historical test results.
✓ Regular test case reviews: Conduct periodic reviews of test cases to identify outdated
or redundant cases and ensure alignment with the evolving API functionality.
✓ Test case automation: Automate repetitive and time-consuming test cases to improve
efficiency, reliability, and maintainability.
18. Have you worked with API automation frameworks? If yes, describe your experience
and the frameworks you used.
• Yes, I have worked with API automation frameworks. Some frameworks I have used
include:
• Postman: Utilized Postman to create and execute API test cases, leveraging its scripting
capabilities and support for environment variables.
• REST Assured: Employed REST Assured, a Java-based library, to automate API testing
and validation, handling request/response interactions, and asserting response data.
• SoapUI: Utilized SoapUI to automate the testing of SOAP and RESTful APIs, including
functional, performance, and security testing.
• Karate: Worked with Karate, an open-source API testing framework, to automate API
tests using a simple domain-specific language (DSL) and support for assertions and
data-driven testing.
• Cypress: Used Cypress, primarily a front-end testing framework, to automate end-to-end
tests involving APIs and user interfaces, performing API requests and assertions within
the test scripts.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
19. How do you collaborate with developers and other team members during API testing?
• Collaboration with developers and other team members during API testing is crucial.
Some collaboration techniques include:
• Participating in sprint planning and design discussions to gain insights into upcoming
API changes or features.
• Engaging in regular meetings or stand-ups to discuss progress, dependencies, and
potential issues.
• Sharing API test plans or strategies with developers to ensure alignment and seek their
input or feedback.
• Providing developers with detailed bug reports or defect information, including steps to
reproduce, logs, and any additional relevant data.
• Collaborating with developers to troubleshoot and resolve API-related issues, sharing
findings and working together to implement fixes.
• Participating in code reviews and offering feedback or suggestions on API
implementation to ensure testability and ease of testing.
• Seeking developers' assistance in understanding complex API functionalities or in
reproducing specific scenarios.
• Contributing to API documentation by providing insights, examples, or clarification on
expected behavior based on testing observations.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
20. Can you share an example of a complex API testing scenario you have encountered
and how you approached it?
Example scenario:
Testing an API that integrated with multiple external services, required complex authentication
mechanisms, and involved intricate data transformations and validations.
Approach:
✓ Analyzed the API documentation and external service integrations to gain a
comprehensive understanding of the scenario.
✓ Collaborated with developers and external service providers to set up the necessary test
environments and access credentials.
✓ Designed test cases to cover various authentication scenarios, including different
authentication providers and tokens.
✓ Implemented test data generation scripts to simulate realistic data for the complex data
transformations and validations.
✓ Utilized mocking techniques and mock servers to isolate testing and avoid reliance on
the availability of external services.
✓ Implemented end-to-end tests to ensure proper integration and data flow between the
API and external
✓ Employed detailed logging and debugging techniques to trace the execution flow,
validate intermediate data transformations, and identify any issues.
✓ Conducted performance testing to measure the API's response time, throughput, and
resource utilization under realistic load conditions.
✓ Collaborated closely with the development team, providing detailed feedback, bug
reports, and suggesting improvements for better integration and performance.
Software Manuel & Automation Test
Engineer (QA Tester)
Abdurrahim Unsal
