The Complete Guide to API Testing

Introduction

Welcome to the world of API testing. If you’re reading this, you’re probably looking to learn the basics of testing APIs or wondering how and where to start. This article will help you understand more about APIs, what types of tests you need to perform, and how to execute them and what to validate as part of the testing process.

What is API Testing?

Application Program Interface testing is a type of software testing that validates the behavior and performance of an application program interface. It is used to ensure that the API functions correctly and meets its requirements. API testing involves sending requests to the server, analyzing responses, and verifying whether they are correct or not. It also involves testing for security vulnerabilities, performance issues, and other potential bugs. By performing API tests, stakeholders can make sure that their applications are functioning as expected.

What is API Test Automation and How Does it Work?

API Test Automation is the process of automating the testing of Application Programming Interfaces (APIs). It is a method of ensuring that APIs perform as intended and are secure from potential risks. Using an API test automation tool, you can rapidly and efficiently test the APIs to uncover any bugs or vulnerabilities before they become problems. This will help us guarantee that the APIs are dependable and secure while also saving time and money in the long term.

Setting up an API Test environment:

It is critical for engineers to set up an API test environment to build and test their applications. It is also critical for organizations to ensure that their APIs are safe and function properly. A local environment ensures confidentiality and anonymity while allowing developers to simply set up, configure, and debug their programs.

Some significant aspects of an API test environment are:

1. Setting up a server
2. Establishing the APIs
3. Creating local accounts for testing
4. Configuring the database
5. Building a virtual environment for the development
6. Integrating other services

Users may easily conduct tests on numerous situations in a well-structured environment before deploying their apps into production.

Types of Output of an API:

When an API is used, the client application can expect a response in one or multiple formats such as JSON, XML, HTML, etc. The different types of response formats provide developers with flexibility when it comes to integrating the data into their projects. Let’s discuss the different types of output formats that an API can provide.

1. XML: Extensible Markup Language is a data format used to create hierarchical structures.

2. JSON: JavaScript Object Notation is a lightweight and human-readable data interchange format used to store and transmit data.

3. HTML: HyperText Markup Language is the primary language used to create web pages and applications.

4. Text: Used to return output in a human-readable string format. Mostly the JSON format will be returned as “Text”.

5. Binary: Used to transmit data in a binary format.

6. Images: Formats such as JPEG, GIF, and PNG can be returned via an API.

Every format has its advantages and disadvantages. Based on the project need and the expected usage of the API, the format should be selected.

Test Cases for API Testing:

When it comes to API testing, the main focus is on verifying the functionality and performance of the API. Basic assertions start from validating the response body, schema, and response codes.

However, other tests need to be performed, such as security testing and performance testing of APIs. 

Here are some of the common types for API testing, based on which test cases can be created:

• Functional Testing: Functional testing for APIs involves verifying that expected responses and data formats are returned given a specific request. This is done by sending requests to an API and validating that the correct responses are returned. This testing should be done to check that new and existing functionality behaves in the expected manner. For example validating the status code and the response body.

• Performance Testing: This type of testing is used to verify that the API can handle large volumes of data and high traffic. Performance testing is used to measure the speed and responsiveness of the API. This is done by monitoring the API’s uptime, response times, and throughput. For instance, verifying the response time and the response size when the API is under load. When we test for multiple users and multiple requests, we are loading the APIs and trying to analyze the performance of the APIs.

• Security Testing: This type of testing verifies that the API is secure and can protect sensitive data and prevent unauthorized access. Security tests are executed to identify security vulnerabilities in an API system, such as cross-site scripting, SQL injection, as well as authentication and authorization controls. The security tests must also identify any security flaws in the infrastructure, such as unencrypted data being transferred or stored, weak passwords, default credentials, and network architecture. 

• API Documentation Testing: This type of testing is used to verify that the API is easy to use and understand and it is performing as mentioned in the API documentation. It ensures that the documentation accurately reflects the APIs capabilities and that all of the features are being properly integrated into the product. With API document testing, testers make sure that the API returns the right data, that the parameters and values are properly set, and that the returned data is in the expected format. This is similar to the functional requirement document/specification document validation against the application behavior.

• Regression Testing: This type of testing is used to verify that changes made to the API do not cause unexpected errors or regressions. Testing typically involves sending requests to an API using a variety of test parameters, ensuring that the appropriate response is sent back and any application or database logic is behaving as expected. The Regression Test suite is built and the API automation is implemented. For instance, the bug related to status code is fixed, then the functional validation is also done for that API endpoint.

• Fault Tolerance Testing: This type of testing verifies the system’s ability to respond accurately and promptly when unexpected failures occur. This is done as part of error-handling scenario validation and how the API responds to inputs or requests that could potentially cause harm, such as a denial-of-service attack, input that is too large or complex to process, or logic errors. It is important to test these potential risks, as it will provide insight into the robustness of the API, ensuring that it can handle unpredictable or malicious inputs without crashing. 

Other than this we can add the test types based on the project needs and requirements specific to the project.

How to Test API?

A few steps are required to test an API. 

Establish a Test Strategy/Plan: The first step is to draft a test plan outlining the tests that will be run. Some projects will require both Test Strategy and Test Plan. Understand more about the API capabilities.

Test Design: The following step is to write test cases for each test in the test plan. Assertions that validate the API’s anticipated output should be included in the test cases. A few example test cases are: 

Validate and check the request parameter values, Validate the response parameters, Validate the response schema

Test Environment: The next step is to prepare the testing environment. This includes configuring the API as well as any tools or libraries required for testing.

Test Execution: The next step is to run the test cases and validate the API result.

Test Reporting: The final step is to report the test findings. Generate reports detailing the results of the executed test cases, including the findings and any issues encountered

Test Maintenance: Conduct regular updates on test data in the designated environment and monitor the APIs for any changes

Best Practices of API Testing

API testing is an important part of the software development process. Here are some best practices for API testing:

• Test Early and Often: Testing should be done early and frequently to discover any possible faults before they turn into a crisis. Once we have the sample responses or endpoints from the developers we can start playing around and try to understand the response and how it’s related to the UI value/fields.


• Use Automation: Don’t stop with testing the endpoints individually. Automation should be utilized to decrease the amount of time and effort necessary to test APIs. So try to automate and build your test suite.


• Write Assertions: Assertions should be used to verify the expected output of the API. Starting from the API’s response time to various requests by analyzing the structure of the response data.


• Test All Endpoints: All endpoints should be tested to make sure that they are working properly. Also, try chaining the requests and testing the data flow.


• Test for Security: Security should be tested to make sure that the API is secure and is protecting sensitive data. For example, when you use the invalid credentials you should be getting 401 Unauthorized response code and the response body should not contain any sensitive information.


• Measure the API Performance: Performance should be examined to make sure that the API can handle big amounts of data and significant traffic.


• Test for Usability: Usability testing validates the design and user friendliness of an API. It determines whether the API can be used easily by its user. Only when it’s easy to read and implement can the APIs be adopted for Integration purposes.


• Test for Compatibility: Compatibility should be tested to make sure that the API is compatible with different platforms, browsers, and devices.


• Regression Testing: APIs should be tested to make sure that changes made to the API (due to defect fixes or new features) do not cause unexpected errors or regressions.

Monitoring: Once you’ve set up your test suite, you should be monitoring test results and updating tests as necessary. Monitoring will help us to track the performance and usage of APIs as traffic and usage grow, allowing them to evaluate prior performance to discover anomalies or patterns, and providing capability for alerting and recording API data.

Challenges of API Testing:

Anyone new to API Testing will have some difficulties getting started. Don’t be concerned. Let’s see in detail the challenges you and your teams face.

1. Lack of Proper API Documentation – The testing team needs to be aware of all the parameters of the API, their types, and the range of valid values. This information is available in the proper documentation, which should be complete and up to date. 

2. Lack of Specialized Skills: API testing requires specific knowledge and experience in API design, development, and testing. The tester must have an advanced understanding of the technology and the language it is written in.

3. Addressing edge cases: API testing tools often struggle to find unexpected or edge cases, which could potentially lead to unexpected behavior in production.

4. Interoperability of Systems: API testing necessitates a detailed grasp of system compatibility. The tester must ensure that diverse systems communicate successfully and that data is transmitted in the desired manner.

5. Versatility Issues – One of the most difficult challenges in API Testing is cross-platform testing, since an API needs to be tested on different platforms, browsers, and devices.

6. Complex Request and response body/formats: When testing APIs, it might be challenging to simulate all message data types. The tester must understand the data formats as well as the various methodologies for testing message formats. It might be challenging to test all possible requests, responses, and combinations.

7. Test Data and API Parameter Combinations: API testing must be done properly and reliably by using appropriate test data. The process of maintaining a trustworthy collection of test data for API testing is known as test data management, and it necessitates careful administration and organization. API testing entails evaluating practically all potential parameter and value combinations, which makes it tough and time intensive.

8. Data Security Issues: API testing should also focus on the security of the data being exchanged. Controlling access and ensuring data integrity is critical. The tester must be aware of authentication, encryption, and authorization processes. 

9. Selection of tools: API testing requires testers to have a good understanding of API testing tools and techniques. This can be challenging when testers are not familiar with scripting languages. And that’s where tools like Testsigma could really help. Testsigma makes it easier for testers. Testsigma lets you automate your tests for web, mobile, desktop and APIs from the same place and is also available as an open-source version.

Start automating your API testing with Testsigma Open Source.

10. Performance Challenges: Performance is an important element in API testing. The tester must be skilled in understanding the appropriate performance criteria for each API. APIs must be tested for response time using various data sets, configurations, and user load. And proper reporting to the stakeholders.

11. Setting up the Test Environments: Configuring an effective and balanced test environment that allows for the stable and accurate testing of APIs can be a challenging task. The test environment must replicate the environment that the API will experience in production, and must provide a stable testing platform with all the necessary resources.

12. Unstable APIs: Newly developed APIs might not be stable. This will require testers to spend more time on the testing and validation process. We must interact often with API developers and comprehend the API’s behavioral pattern.

13. Error handling scenarios: API testing includes verifying the error codes for different scenarios. Getting to know all the error codes is really challenging. Also covering all the scenarios is a complex task.

API Test Automation Strategies & Techniques for Optimizing Quality

1. Implement End-to-End Tests: End-to-end testing entails mimicking user journeys and the API calls that go with them through your release candidate. This helps to verify that all functionality is functioning and tested before going live.

2. Utilize Automation Tools: Don’t stop testing the API endpoints manually. Automation ensures that tests are done at scale and can speed up the API testing process.

3. Monitor Your API Performance: Automated monitoring aids in the detection of regressions and the identification of performance bottlenecks. You can monitor API performance down to the request and response level with tools like Elastic APM. You may configure alerts to be triggered in the case of severe swings in performance, allowing you to take remedial action swiftly.

4. Leverage Post-Deployment Testing: This enables you to understand how an API is employed in reality and detect any bugs with its implementation or new features that have been added. Initially, this should be done manually, but as the platform evolves, it may be automated.

5. Utilize Endpoint Coverage Analysis: This allows you to ensure that your API tests cover the whole endpoint and test all potential states and scenarios. Read more about it here: https://personal.us.es/amarlop/wp-content/uploads/2019/09/Test_Coverage_Criteria_for_RESTful_Web_APIs.pdf

API Testing Tips for Beginners:

If you’re new to API testing, here are some tips to help you get started:

• Understand the Basics: It’s important to understand the basics of API testing, API-related jargon, such as the different types of tests that need to be performed and the different types of output that can be expected.

• Start small and simple. If you are new to API testing, start by testing a few basic API calls before moving on to more complex ones. Pick tools like Testsigma and play around the public APIs. Any API is a good repository of public APIs. 

• Understand API requirements/capabilities: Ensure you have a clear understanding of the API, its inputs, its outputs, and any underlying protocols or technologies involved.

• Use the Right Tools: The right tools are essential for API testing. Make sure to use the right tools for the job Testsigma is easy to use and feel free to try the tool.

• Create a Test Plan: Create a test plan that outlines the tests that will be performed and the expected output. You can think about the dependencies and risks and detail them.

• Utilize API debugging tools – API debugging tools can help you simulate API requests for API testing. If you are running into any issues with API requests, use API debugging tools to quickly identify and troubleshoot the problem.

• Do your research: Maintain your curiosity for learning new technologies and stay up to date on API developments.

Start your API Testing journey with ease with Testsigma

Automating your API test cases is very easy with Testsigma. 

For example, lets see how to automate a simple API test to “Test the Expected Response Status Code for a GET request”

1. To begin with, we will have to make the following entries in Testsigma:

URL: https://jsonplaceholder.typicode.com/users

HTTP Method: GET

Test: Status Code

Expected Status Code: 200

2. The Request Details would be added in an API test case in Testsigma, it would look like the screenshot below:

The response that needs to be verified will be added under “Verify Response” and will look something like below:

And with just this much effort, the automated test case is ready for execution. When the test case will be executed, if the response code matches the expected status code, the test will pass. And, if it does not, the test will fail.

Read more here: https://testsigma.com/tutorials/getting-started/automate-rest-apis/

Closing thoughts:

We are about to conclude. Yes, it’s pretty long and informative, right? Let’s have a recap.

1. Pick an API testing tool.


2. Create the necessary resources for the test environment, such as test databases, mock services, and testing accounts.


3. Identify the test cases that must be automated and establish input parameters such as headers and queries, as well as test cases.


4. Write short and extensive scripts that include assertions to test various API endpoints.


5. Create test cases to put the API through its tests with the supplied parameters.


6. Write a test report and save it in your project’s repository.


7. Run the test cases and analyze the results to validate the API.


8. Have the API tests automated.


9. Review the test findings and monitor the API on a regular basis.

We hope you found our API Testing tutorial informative. API testing may be challenging, but with the correct tools and best practices, it can be done easily. So, if you follow the pointers mentioned in this article, you’ll be well on your way to being an API testing pro!

Frequently Asked Questions:

How do I test my local API?

The easiest way to test your local API is to use tools such as Testsigma.  These tools allow you to run GET, POST, PUT, and DELETE requests to your local endpoint, which can be useful for verifying that your API is working properly.

How do you check if an API is working?

1. Start by sending a GET request to the API’s service URL. This is usually done by typing in the URL into a web browser or using a REST client such as Postman.

2. If the API is working, you should receive a response in the form of a 2XX status code and a related message. 

3. If the API is not working, you may see a different status code indicating the error.

4. Once you have established that the API is working, you can begin making requests to specific endpoints and parameters within the API.

What is the best API testing method?

The best API testing method depends on your project’s needs, but some of the most popular methods include unit testing, integration testing, functional testing, stress testing, and performance testing. Each of these methods offers unique benefits and each should be evaluated for its specific use case. A combination of multiple API testing methods will provide the most comprehensive results.

PC: Freepik