API testing is a type of software testing that focuses on verifying the functionality and reliability of APIs. It involves testing the request and response of API calls, ensuring that the API works as expected.
Here are top API testing interview questions,
1. What is the purpose of API
documentation, and how can it aid in testing?
API
documentation provides detailed information about API endpoints, request
formats, response structures, and usage examples. It aids testing by helping
testers understand how to interact with the API correctly and by serving as a
reference for expected responses.
2. What are the key advantages of
API testing over GUI testing?
API testing
has several advantages, including:
- Faster execution, as there's no need for a
graphical user interface.
- Greater test coverage, as APIs often have
more functions and endpoints.
- Improved test stability, as APIs tend to
have less frequent changes than UIs.
- Better support for automation due to
structured data formats like JSON or XML.
3. What are some common types of
APIs that you might encounter in testing?
You may
encounter various types of APIs, such as:
- HTTP APIs (REST and SOAP): Used for web
services.
- Library APIs: Used for programming
language libraries.
- Database APIs: Used for database
connectivity.
- Hardware APIs: Used for device
interaction.
- Third-party APIs: External services like
payment gateways or social media integrations.
4. How can you test RESTful APIs?
To test
RESTful APIs, you can perform the following actions:
- Send HTTP requests (GET, POST, PUT, DELETE)
to API endpoints.
- Validate the status code of responses
(e.g., 200, 404, 500).
- Check response headers for required
information.
- Verify the response body for data
correctness, using tools like JSONPath or XPath.
5. What are the HTTP status codes
commonly used in API testing, and what do they signify?
Common HTTP
status codes in API testing include:
- 200 OK: Successful request.
- 201 Created: Resource created
successfully.
- 204 No Content: Successful request with no
response body.
- 400 Bad Request: Invalid request format or
parameters.
- 401 Unauthorized: Authentication required
or invalid credentials.
- 403 Forbidden: Authentication successful
but access is denied.
- 404 Not Found: Resource not found.
- 500 Internal Server Error: Server-side
error.
6. What is the purpose of an API
endpoint?
An API
endpoint is a specific URL or URI that an API exposes for interacting with a
particular resource or functionality. It defines the path and method (e.g.,
GET, POST, PUT, DELETE) to access that resource.
7. How do you handle authentication
in API testing?
Authentication
in API testing can be handled through methods like:
- Basic Authentication: Sending a username
and password in the request headers.
- API Keys: Using unique keys provided by
the API.
- OAuth: For secure authorization and access
token management.
- Bearer Tokens: Including a token in the
request headers.
- JWT (JSON Web Tokens): Used for secure
authentication and data integrity.
8. Can you explain the difference
between stateful and stateless APIs?
Stateful
API: The API server maintains the client's state between requests. Each request
relies on the previous one, and the server stores client-specific information.
Stateless
API: Each request from a client to the server is independent, and the server
doesn't store client-specific data between requests. The client includes all
necessary information in each request.
9. What is POSTMAN, and how can it
be used in API testing?
POSTMAN is
a popular tool for API testing and development. It allows testers to:
- Send HTTP requests and view responses.
- Create and organize API requests in
collections.
- Automate API testing using scripts.
- Generate API documentation.
10. What is the difference between
SOAP and REST APIs?
- SOAP (Simple Object Access Protocol):
Protocol-based, uses XML for requests and responses, often requires a rigid
contract (WSDL), and has built-in security.
- REST (Representational State Transfer):
Architectural style, uses various data formats (JSON, XML, HTML), relies on
HTTP methods, and is more flexible.
11. What is API versioning, and why
is it important?
API
versioning is the practice of managing different versions of an API to ensure
backward compatibility while introducing new features or changes. It's
important to avoid breaking existing client applications and maintain a stable
interface.
12. What is rate limiting in API
testing, and why is it necessary?
Rate
limiting is a mechanism to control the number of API requests a client can make
in a given time frame. It's necessary to prevent abuse, ensure fair usage, and
maintain the API's performance and availability.
13. Explain the concept of mocking
in API testing.
Mocking
involves simulating an API's behavior without actually making real network
requests. It's used to isolate the unit under test and create controlled
environments for testing when real API access is not possible or desirable.
14. How do you handle API testing
for non-functional aspects like performance and security?
- Performance Testing: Use tools like Apache
JMeter or Gatling to simulate concurrent requests and measure response times.
- Security Testing: Perform security tests
for vulnerabilities like SQL injection, Cross-Site Scripting (XSS), and ensure
data encryption using tools like OWASP ZAP or Nessus.
- To ensure API security, you can:
·
Perform
security testing to identify vulnerabilities.
·
Implement
proper authentication and authorization mechanisms.
·
Encrypt
sensitive data.
·
Keep
API keys and credentials secure.
·
Monitor
and log API activities for anomalies.
15. What are some challenges you
might encounter in API testing, and how can you overcome them?
Challenges
include:
- Lack of Documentation: Rely on available
information and explore the API.
- Changing APIs: Use versioning, test
automation, and continuous monitoring.
- Complex Data Formats: Develop parsers for
handling complex data structures.
- Authentication Issues: Verify credentials
and tokens meticulously.
16. How can you ensure data
integrity in API testing?
Data
integrity can be ensured by:
- Comparing API responses against expected
results.
- Using checksums or hashing for data
validation.
- Testing edge cases and boundary values to
identify issues.
17. What is API contract testing,
and why is it important?
API
contract testing involves verifying that the API adheres to a predefined
contract or specification. It ensures that changes to the API do not break
existing functionality, making it crucial for maintaining backward
compatibility.
18. What is the purpose of API
monitoring, and what tools can be used for it?
API
monitoring continuously checks the availability, performance, and functionality
of APIs in production. Tools like New Relic, Pingdom, or custom scripts can be
used for API monitoring.
19. What is the role of automation
in API testing, and which testing frameworks are commonly used?
Automation
is vital for API testing. Popular testing frameworks include:
- JUnit and TestNG: For Java-based API
testing.
- pytest: For Python-based API testing.
- RestAssured: A Java library for REST API
automation.
- Karate: A framework for API testing and
automation using Gherkin syntax.
20. Describe the typical workflow of
API testing in a CI/CD pipeline.
In a CI/CD
pipeline, API testing involves:
- Triggering API tests on code commits or
deployments.
- Running tests against various environments
(e.g., staging, production).
- Generating reports for test results.
- Integrating with version control, CI
tools, and monitoring systems for automated feedback.
Above are few top API testing interview questions. Remember to prepare and expand on these answers.
Good luck with your interview! 👍
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