Creating Test Cases for API Functional Testing 

Creating Test Cases for API Functional Testing 

Creating test cases for API functional testing involves defining scenarios that validate the correctness, completeness, and performance of the API. Here’s a guide on how to structure and create effective test cases for API functional testing.

1. Understand API Requirements #

• API Documentation: Start by thoroughly reviewing the API documentation. Understand the endpoints, request methods (GET, POST, PUT, DELETE), parameters, headers, request bodies, response bodies, status codes, and any constraints or preconditions.

2. Identify Test Scenarios #

• Positive Test Cases: Test cases that validate the API works as expected with valid inputs.
• Negative Test Cases: Test cases that validate how the API handles invalid inputs, incorrect methods, missing parameters, etc.
• Boundary Test Cases: Test cases that check the API’s behavior at the boundaries of input ranges.
• Error Handling: Test how the API handles various error conditions, like missing or incorrect authentication, invalid data formats, and unauthorized access.

3. Structure of a Test Case #

Each test case should be clearly defined and include the following elements:

• Test Case ID: A unique identifier for the test case.
• Title/Description: A brief description of what the test case will validate.
• Preconditions: Any setup or conditions that must be met before the test can be executed (e.g., authentication token required).
• Test Steps: Step-by-step instructions on how to execute the test, including endpoint, method, parameters, headers, and body.
• Expected Result: The expected outcome, including status code, response body, headers, etc.
• Actual Result: The actual outcome when the test is executed.
• Pass/Fail Criteria: The conditions under which the test case is considered to have passed or failed.

4. Sample Test Cases #

Test Case 1: Validating Successful User Login (Positive Test Case) #

• Test Case ID: TC001
• Title: Validate successful login with valid credentials
• Preconditions: User account exists with a valid username and password

• Test Steps:

1. Send a POST request to /login.
2. Set the Content-Type header to application/json.
3. Include the following JSON payload:
   

{
     "username": "valid_user",
     "password": "valid_password"
}

• Expected Result:

1. Status Code: 200 OK
2. Response Body:

{
	"token": "abcdef123456",
	"message": "Login successful"
}

3. Headers: Content-Type should be application/json

• Pass/Fail Criteria: Test passes if the status code is 200, and the response body contains a valid token and success message.

Test Case 2: Handling Login with Invalid Credentials (Negative Test Case) #

• Test Case ID: TC002
• Title: Validate response for login with invalid credentials
• Preconditions: User account does not exist or credentials are incorrect
• Test Steps:
  • Send a POST request to /login.
  • Set the Content-Type header to application/json.
  • Include the following JSON payload:

{
	"username": "invalid_user",
	"password": "invalid_password"
}

• Expected Result:
  • Status Code: 401 Unauthorized
  • Response Body:

{

"error": "Invalid username or password"

}

• Headers: Content-Type should be application/json

• Pass/Fail Criteria: Test passes if the status code is 401, and the response body contains an appropriate error message.

Test Case 3: Validating Required Fields (Boundary Test Case) #

• Test Case ID: TC003
• Title: Validate API response when required fields are missing
• Preconditions: N/A
• Test Steps:
  • Send a POST request to /register.
  • Set the Content-Type header to application/json.
  • Include the following JSON payload with the missing “password” field:     

{
     "username": "new_user"
}

• Expected Result:
  • Status Code: 400 Bad Request
  • Response Body:

{
    "error": "Password is required"
}

• Headers: Content-Type should be application/json

• Pass/Fail Criteria: Test passes if the status code is 400, and the response body indicates the missing field.

Test Case 4: Validating Response Time (Performance Test Case) #

• Test Case ID: TC004
• Title: Validate that the API response time is within acceptable limits
• Preconditions: N/A
• Test Steps:
  • Send a GET request to /data.
• Expected Result:
  • Status Code: 200 OK
  • Response Time: < 500ms
  • Response Body: Valid JSON data
• Pass/Fail Criteria: Test passes if the response time is less than 500ms and the status code is 200.

5. Automating API Test Cases #

• Use tools like Postman, RestAssured, or Cypress to automate API testing.
• Implement continuous integration (CI) with tools like Jenkins or GitHub Actions to run API tests as part of the build pipeline.

6. Review and Update #

• Regularly review test cases to ensure they remain relevant and up to date with API changes.
• Update test cases as new features are added or as bugs are fixed.

Summary #

Creating effective test cases for API functional testing involves understanding the API, identifying test scenarios, structuring test cases properly, and using tools for execution and automation. Testing should cover all functional aspects of the API, including positive and negative scenarios, boundary conditions, error handling, and performance.