Writing Baseline Test Coverage for APIs

APIs (Application Programming Interfaces) are critical for enabling communication between software applications. This is use mostly in the Open Bank world (Fintech). Ensuring the reliability and correctness of APIs is vital, and one way to achieve this is through baseline test coverage. Baseline tests serve as the foundation for maintaining the quality and stability of an API.

This article will provide a detailed insight on writing baseline test coverage for APIs, focusing on best practices, tools, and practical examples. Understand that though these tools vary, they can still be used to achieve the same goal this article is centered on. You should test all if you can to know that meet your expectations or requirement as they have some features that makes them different.

What Is Baseline Test Coverage?

Baseline test coverage refers to the minimum set of test cases that ensure an API’s basic functionality works as intended. These tests verify core functionalities, error handling, and response consistency. Baseline coverage acts as a safeguard against regressions and helps identify critical issues early in the development lifecycle.

Steps to Write Baseline Test Coverage for APIs

1. Understand API Requirements and Specifications

• Review Documentation: Gather detailed information about the API endpoints, request parameters, response structure, and authentication methods. As a developer or technical engineer, you may be quick to grab things but reading an API Documentation is very key to your job success or usage of that API.
• Define Success Criteria: Clearly outline what constitutes a successful response for each endpoint. Always document what you need and know if what you get is exactly what you order, in Instagram voice, "what you get vs what you order."

2. Identify Critical Endpoints and Operations

Not all endpoints need the same level of coverage initially. Prioritize critical endpoints based on:

• Frequency of use.
• Business importance.
• Dependencies with other systems.

Noting down this will help you with your security check as well.

3. Set Up the Testing Environment

• Environment Configuration: Ensure a consistent testing environment (e.g., staging server) that mirrors production.
• Authentication: Prepare API keys, tokens, or credentials required for secure access.
• Mock Servers: Use tools like Postman Mock Servers or WireMock to simulate responses for isolated testing.

4. Write Test Cases for Core Functionalities

Include the following categories:

a. Positive Tests

Verify the API’s expected behavior for valid inputs.

• Example: Sending valid data to a POST /user endpoint should return a 201 Created response with the user’s details.

b. Negative Tests

Check how the API handles invalid or unexpected inputs.

• Example: Sending a malformed JSON payload to a POST /user endpoint should return a 400 Bad Request response with an appropriate error message.

c. Boundary Tests

Test the limits of the API’s parameters.

• Example: Submitting the maximum allowed characters in a username field to ensure it’s accepted.

d. Error Handling Tests

Validate the API’s responses for various error scenarios.

• Example: Accessing a non-existent resource via GET /user/9999 should return a 404 Not Found response.

e. Performance Baseline Tests

Measure the API’s response time and throughput under normal load conditions.

• Example: Ensure that the GET /products endpoint responds within 200ms for 90% of requests.

5. Automate Testing

• Use API testing tools like Postman, REST Assured, or Karate to automate test execution. (PS: I love using Postbot for writing my test script)
• Integrate test scripts with CI/CD pipelines for continuous validation.

6. Document the Tests

Maintain a clear and concise test suite documentation that includes:

• Purpose of each test.
• Input parameters and expected outputs.
• Dependencies and setup instructions.

Best Practices for Writing Baseline Test Coverage

1. Focus on High-Impact Areas: Concentrate efforts on the most critical and frequently used endpoints first.
2. Adopt a Layered Approach: Combine unit tests, integration tests, and end-to-end tests for comprehensive coverage.
3. Keep Tests Independent: Ensure each test case is self-contained to avoid dependencies that could lead to false failures.
4. Use Realistic Data: Employ data that closely mimics real-world scenarios to uncover practical issues.
5. Leverage Versioning: Maintain separate test suites for different API versions to avoid conflicts and ensure backward compatibility.
6. Monitor and Update: Regularly review and update baseline tests as the API evolves or new features are added.

Example Baseline Test Case

Test Name: Validate User Creation (This is a scratch example; you can get more via Postman Academy)

• Endpoint: POST /users
• Purpose: Verify that a new user can be successfully created.
• Steps:

1. Send a POST request with valid user details:

{
  "name": "John Doe",
  "email": "[email protected]",
  "password": "JohnDoeNeverDies"
}        

2. Assert the status code is 201 Created.

3. Validate the response body contains the user ID and other submitted details.

4. Ensure the Location header points to the newly created resource.

• Expected Result:

{
  "id": lovec165-2741-c6f3-9ccc-u06e1876,
  "name": "John Doe",
  "email": "[email protected]"
}        

Tools for API Testing (Based on some uniqueness I find using them)

1. Postman: For manual and automated API testing. (Easy go to)
2. Swagger: For documentation-driven testing.
3. JMeter: For performance and load testing. (I use this for rarely, all I can tell you is don't start learning about API testing with this.)
4. REST Assured: For Java-based API testing.
5. Karate: A DSL-based testing framework for APIs.

Conclusion

Baseline test coverage is the cornerstone of a robust API testing strategy. By focusing on critical functionalities, handling both positive and negative scenarios, and leveraging automation, teams can ensure that their APIs are reliable and performant. Regularly revisiting and expanding baseline tests as the API evolves will further enhance its stability and trustworthiness.

If you are a founder or creative and you want to delve into the fintech world or provide banking service to your niche or recognized market use Maplerad . Their API are reliable and great.

Thanks for reading.