Fundamentals of Testing

API testing, or Application Programming Interface testing, is a type of software testing that involves testing the interfaces between different software components. It ensures that the API functions correctly in terms of data accuracy, response time, and overall performance. Here's a general procedure for API testing, along with some real-life examples:

Understand the API Requirements:

1. Gather documentation: Obtain API documentation that includes details about endpoints, request methods, request/response formats, authentication methods, and error handling.

Set Up Test Environment:

1. Create a test environment that mirrors the production environment.
2. Deploy the API on a test server or use a staging environment.

Identify Test Scenarios:

1. Define test scenarios based on functional requirements, business logic, and use cases.
2. Include positive and negative scenarios to cover a wide range of possibilities.

Perform Functional Testing:

1. Test API endpoints for correctness, data accuracy, and adherence to specifications.
2. Verify the response codes, headers, and payload content.

Test Data:

1. Use various types of input data to test different scenarios.
2. Include boundary values, edge cases, and invalid inputs.

Security Testing:

1. Perform security testing to ensure that the API is protected against common vulnerabilities such as SQL injection, cross-site scripting (XSS), and unauthorized access.
2. Test for proper authentication and authorization mechanisms.

Performance Testing:

1. Check the API's performance by sending a large number of requests to evaluate response times and scalability.
2. Conduct stress testing to assess the API's ability to handle a high volume of concurrent requests.

Error Handling:

1. Test how the API handles errors by providing incorrect inputs or triggering specific error conditions.
2. Ensure that error responses provide meaningful information for debugging.

Automation:

1. Implement automation tools and frameworks to streamline repetitive and complex test scenarios.
2. Popular tools for API testing include Postman, REST Assured, and Swagger.

Regression Testing:

1. Perform regression testing after each code change to ensure that existing functionalities still work as expected.
2. Automated tests can help in efficiently executing regression tests.

Documentation and Reporting:

1. Document test cases, test results, and any issues discovered during testing.
2. Provide clear reports to stakeholders with details on test coverage and pass/fail status.

Real-Life Example:

Let's consider a hypothetical scenario of testing a weather API:

Scenario 1 (Positive Test):

1. Test Endpoint: /weather/{city}
2. Input: Valid city name (e.g., "New York").
3. Expected Output: Valid weather information for the specified city.

Scenario 2 (Negative Test):

1. Test Endpoint: /weather/{city}
2. Input: Invalid city name (e.g., "xyz123").
3. Expected Output: Proper error response with a clear message indicating that the city was not found.

Scenario 3 (Performance Test):

1. Test Endpoint: /weather/{city}
2. Input: Valid city name.
3. Expected Output: Evaluate response time under varying levels of concurrent requests to ensure the API can handle peak loads.