21. What are common API errors that are often encountered?
In API testing, several types of common errors are frequently identified:
- Missing Module Errors: This occurs when certain functionalities/modules expected to be present are missing due to misconfiguration or incomplete deployment.
- Documentation Errors: Incorrect or outdated documentation can lead to misunderstanding of API behavior, resulting in incorrect API usage.
- Parameter Validation Errors: These happen when APIs do not correctly validate inputs like missing required parameters, incorrect data types, or invalid values.
- Unexpected Results and Warnings: APIs often return unexpected results if there are bugs in backend logic. In such cases, warning messages might also be returned.
- Multiple Warnings per Module: A single module might generate multiple warnings related to business logic validation, data integrity, or performance issues.
In real-world scenarios, an API tester must not only detect these errors but also log, report, and reproduce them clearly for development teams.
22. What kinds of bugs does API testing commonly find?
API testing can uncover a variety of bugs that are critical to system stability and performance:
- Missing or Duplicate Functionality: API endpoints may not perform as documented, or unintended duplications might exist.
- Poor Error Handling: APIs might crash or return non-informative errors when invalid input is provided instead of handling errors gracefully.
- Stress and Load Issues: Under heavy load, APIs might slow down, time out, or crash.
- Reliability Bugs: Failures when API requests are repeated multiple times or run over extended periods.
- Security Flaws: APIs might expose data improperly, have authentication vulnerabilities, or suffer from injection attacks.
- Unused Flags or Features: Features that are partially developed or obsolete but not removed.
- Unimplemented Features: API endpoints returning 501 (Not Implemented) due to incomplete development.
- Inconsistent Error Codes or Messages: Different modules returning different formats or codes for similar errors.
- Performance Degradation: High response times, inefficient queries, or poor resource usage.
- Multi-threading Issues: Concurrency bugs when APIs handle simultaneous requests improperly.
Summary: API testing does much more than just verify correct data — it deeply checks reliability, security, and performance aspects.
23. What is API documentation?
API Documentation is a technical manual that provides a detailed guide on how developers should interact with an API. It includes:
- Endpoints: List of available services and resources.
- Methods: Supported HTTP methods like GET, POST, PUT, DELETE.
- Input/Output Schema: What parameters are required, optional, and their data types.
- Response Details: Success and error responses with status codes.
- Authentication: How to authenticate and authorize API access.
- Examples and Tutorials: Real examples of request/response to guide developers.
A well-written API documentation improves developer experience, reduces integration time, and ensures API adoption is smooth and error-free.
24. What are API documentation templates commonly used?
To simplify the creation of API documentation, several popular templates and tools are used:
- Swagger/OpenAPI: Auto-generates interactive API documentation with try-out options.
- Miredot: A tool for generating REST API documentation for Java applications automatically.
- Slate: Provides clean, beautiful static documentation for REST APIs.
- FlatDoc: A minimalistic tool to create API docs using Markdown.
- API Blueprint: Allows structured API description and documentation via Markdown-like syntax.
- RestDoc: Focuses on producing documentation for RESTful web services.
- Web Service API Specification: General guideline documents like WSDL for SOAP APIs.
Key Tip: Mastering Swagger/OpenAPI is highly recommended as most companies use it!
25. When writing API documentation, what must be considered?
While preparing API documentation, always consider:
- Source of Content: Gather information from technical specifications, user stories, and developer interviews.
- Document Structure/Sketch: Plan the sections beforehand like Introduction, Authentication, Error Codes, Endpoint Details, etc.
- Delivery Layout: Choose readable, user-friendly formats — HTML pages, PDF manuals, or live Swagger UIs.
- Information for Every Function: Cover method type, parameters, data formats, sample requests/responses, and possible error codes.
- Automatic Documentation Tools: Integrate tools like Swagger-UI to generate real-time updatable documentation based on the API code.
In short, clarity, completeness, and usability are the pillars of excellent API documentation.
26. How often are APIs changed or deprecated?
APIs, especially public or enterprise-level APIs, can change frequently because of:
- Business Needs: New requirements may demand changes or additions to APIs.
- Security Updates: Vulnerabilities require changes to API behavior or endpoints.
- Performance Improvements: APIs might be redesigned to be faster and more scalable.
- Third-party Integration Updates: Changes in dependencies like payment gateways, authentication providers force API changes.
Deprecation:
When an API version is no longer recommended for use, it is deprecated. Developers are usually informed via deprecation warnings before the actual shutdown.
Best Practice: Always track API version changes, deprecation notices, and migration guides actively.
27. What is REST?
REST (Representational State Transfer) is an architectural style for building scalable web services using standard HTTP methods. Key ideas:
- Resources: Everything (documents, images, services) is treated as a resource.
- Uniform Interface: All resources are accessed uniformly using HTTP verbs.
- Stateless Communication: Each request from a client contains all information necessary.
- Representation: Resources can be represented using formats like JSON, XML, etc.
- Client-Server Separation: Clear separation of concerns improves scalability.
REST APIs are highly popular because they are simple, lightweight, and easy to integrate.
28. What is a RESTful Web Service?
A RESTful Web Service is a web service that:
- Adheres to REST principles.
- Uses HTTP methods explicitly (GET, POST, PUT, DELETE).
- Uses URIs to uniquely identify resources.
- Transfers data using lightweight formats like JSON and XML.
Comparison with SOAP:
While SOAP uses XML only and is heavy, RESTful services are simple, scalable, and flexible.
29. What is a “Resource” in REST?
In REST:
- A resource is any information or object accessible via a URI.
- Examples: A document, an image, a user profile, a product, etc.
- REST server provides representations (usually JSON/XML) of the resource, and clients interact with them.
Example:
https://api.example.com/users/123 → represents the user with ID 123.
30. What is the most popular way to represent a resource in REST?
JSON is the most popular format today because:
- Lightweight compared to XML.
- Easier for web applications to parse and render.
- Readable for humans and machines.
However, XML is still used in legacy systems and when strict schema validations are required.
👉The Next 10 Questions-II: API TESTING
