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Vladyslav Bilous, Automation Quality Assurance Engineer

Sep 19, 2023 17 min read

How to Automate API Testing: Tips and Best Practices

An API is a set of rules and protocols developers use to integrate application software into existing systems and platforms. These systems simplify data exchange between application components, allowing efficient work with remote requests. An API provides a predictable and understandable way to communicate between systems, which increases development speed and helps avoid project delays. In this article, you'll explore how to automate API testing.

How to Automate API Testing

What is API, and why should it be tested?

API testing analyzes an API and ensures that it works as expected, performing its functions reliably without any negative impact on performance.

API testing is essential for several reasons:

  1. Ensuring correctness of functionality: API defines how different software components interact. By performing API testing, we ensure that this interaction works correctly and that the software functions as expected.  
  2. Ensuring reliability: Predictable and stable operation of the API is an essential factor for the reliability of the software as a whole. API testing helps identify potential problems and helps ensure that the software will work stably under different conditions. 
  3. Ensuring security: APIs can become a potential entry point for attackers, so API testing helps identify potential vulnerabilities and protect software from attacks. 
  4. Support for backward compatibility: APIs can change over time, and API testing ensures that changes do not break backward compatibility with existing applications and systems that use this API.

API testing is a critical step in software development that helps ensure a product's quality, reliability, and security before it is released to the market. Learn more about software API testing and how it can optimize your development process.

API Testing in the Test Pyramid

The test pyramid is a structure that can help developers and quality assurance professionals create high-quality software by structuring the testing process in levels. At the first level are unit tests performed by developers while writing code. The next level is server-side testing (Integration tests), which includes API testing. In the end, UI testing takes place when the frontend is ready.  

UI testing can only cover some aspects of backend testing and is often insufficient to test functional paths and API services. We need help to detect most of the backend bugs or even at the level of code units, leading to a significant increase in the cost of errors and delays in product release.

An intelligent solution is to start testing early in development. If the query does not return the required value at the server level, it will not be displayed in the user interface. Performing API tests in the initial stages of development allows you to identify and eliminate at least half of the errors before they become serious problems. Learn how Luxe Quality helped CultBooking optimize their software quality with our comprehensive testing services.

Types of API 

Knowing the basic API types is critical to successfully using them. API typing helps define the structure and format of the data that the API accepts and returns. Let's first consider typing by access: 

  1. Public APIs: Developers create these APIs for their applications and provide access to the world. Such APIs are often commercialized for additional revenue; for example, the Google Maps API is used by Google.   
  2. Private and Internal APIs: These are limited only for internal use. Companies use them to communicate between their programs, ensuring internal efficiency.  
  3. Partner APIs: Developers create these APIs specifically for partners and share access only with them. It can be an API for working with databases, CRM systems, or email services. 
  4. Complex APIs: Consists of multiple APIs to perform sequential actions. Complex APIs are usually created because they are faster than one extensive API. 

Knowing how to type APIs by access helps testers test effectively (for example, public APIs may require robustness tests to many requests, while private APIs require security and authorization tests), select appropriate tools, and ensure test accuracy and reliability.

APIs share data and functions, requiring clear protocols and architectures – the rules by which the API will operate. There are three main types of API architectures: RPC, REST, and SOAP.  

  1. RPC (Remote Procedure Call): This type of architecture sends parameters and receives results from actions or processes. The RPC API allows you to call functions or methods from remote execution. Using data formats such as JSON or XML, you can transfer data between applications. The RPC API is suitable for internal components of complex systems where speed and interoperability are critical. 
  2. SOAP (Simple Object Access Protocol): SOAP is a more structured and controlled format for exchanging data. Using only XML it provides a strict specification for communication between programs. SOAP is famous for internal or partner APIs where security and defined rules are essential considerations. 
  3. REST (Representational State Transfer): REST is a simpler alternative to SOAP. It uses unique URLs to share data. Each resource or feature has its URL that can be invoked to retrieve data or perform actions. Rest API automated testing is well-suited for simple and large databases, making it popular for public APIs such as mobile applications.

You can expand your understanding of API architectures with the following table: 




Principle of operation 

Procedure call

Sending a message in a strict format 

Sending a message as a resource


JSON, HML, Protobuf, Thrift 

XML only

XML, JSON, HTML, simple text 

Where is it used? 

Complex APIs or internal microservices

Payment systems and identification in financial systems

Public APIs 

Knowing the variety of API architectures and their features, it will be much easier to answer how to automate API testing. Therefore, standard general knowledge cannot be ignored.

Manual VS automated API testing

In this section, we'll look at which approach to API testing – automated or manual – might be most effective for your project.

Manual API testing

Manual API testing is a method where specialists manually test the functionality of the API. This process involves writing your query to integrate with the API and test its functionality.

Advantages of manual API testing  

Manual API testing has its advantages, especially in certain situations where it is essential to have a flexible and accurate testing approach.

  1. Search testing. Manual testing is the ideal solution in the initial stages of learning how the API works. It allows you to quickly make changes to the query and test the API at an early stage of development. This approach helps identify possible problems and make minor adjustments to the code. 
  2. Testing secondary functions. Some specific test scenarios are best done manually, especially if they allow efficient problem detection and resolution. 

Problems with manual testing REST APIs 

While manual API testing has advantages, it also comes with some challenges, especially regarding REST APIs.

  1. Scale. An automated testing process may be more efficient for larger projects. 
  2. Accuracy. The accuracy of manual testing depends on the tester's experience level. An inexperienced QA may need help to test the API accurately.

Automated API testing

With automated API testing, you can test everything from security and performance to functionality and resource efficiency. The automated testing process sends test queries to an API and analyzes the responses. Some automated testing programs support custom tests, configuration, and analysis of results. Read about our collaboration with QPilot- to see how we helped streamline API testing processes for improved efficiency and reliability.

Benefits of automating API testing 

Automation of API testing has many advantages over manual testing:

  1. Greater accuracy. The automated system methodically reviews the code and tests every function similarly. This provides a higher level of accuracy of the results and helps to detect errors. 
  2. More effective time. Automated testing speeds up the testing process and helps to save the tester's time.

Problems with API automation

Although automated testing has many advantages, there are some challenges:

  1. Complex APIs. Testing complex APIs requires more time and resources due to the need for complex tests and tools. 
  2. Data in real-time. Some APIs work with actual data, which can cause unique problems and affect the testing process.

What and when to choose?  

Manual testing is much more practical, making it an ideal tool for testing APIs at complex levels of detail to ensure a good level of performance. On the other hand, the speed and reliability of automated testing make it ideal for complex APIs and large amounts of data, and it can be executed in various scenarios and test configurations. While manual testing thrives in the early stages of coding and determining the progress of a simple API, automated testing is ideal for the pre-release setup of a larger and more complex product. An API check will automatically occur after deploying integrated CI/CD process changes.

How to do API testing?

Step 1: Define Requirements for API 

Start by clearly understanding the purpose and target consumer of the API. Define the main aspects and functionality of the API and how it interacts with other APIs. Carefully plan your test scenarios, identify the issues you plan to test, and prioritize your testing. This stage defines exactly what the API expects on the entrance and what response reflects its success.

Step 2: Preparing the Test Environment for the API

Set up a test environment for the API, including servers, databases, and other resources that your application interacts with through the API. Ensure that this environment meets the requirements of your software and reflects real-world operating conditions.

Step 3: First API Test Call

Before proceeding with detailed testing, make a test call to the API to ensure it responds to requests.

Step 4: Defining Input Parameters

Plan all possible variations of the input parameters that will be used in the test cases. This is important for determining whether the API matches the documented requirements for different input scenarios. 

Step 5: Creating API Test Scripts  

Finally, write and execute test scripts for the API. We recommend grouping tests by categories, including checking values in response to different input conditions, analyzing system behavior under different scenarios, the impact on the system after data changes, and checking changed resources.

This systematic approach will allow you to efficiently and accurately test your API, ensuring your software product's reliability and high quality. 

How to automate API testing: API testing automation best practices from our experts 

A deep understanding of these practices will help you perform testing most optimally, guaranteeing that the final product meets the documented requirements. 

Test API with valid data

Test API with valid data first. This means loading the API with standard parameters under normal conditions without using excessive test environment settings. This phase tests the basic functionality of the API and the application, identifying possible fundamental problems in the underlying code.

Recommendation: Run valid tests regularly before each release and after changes to make sure core functions are running smoothly. 

Test the limits of your system 

After confirming essential performance, move on to limit testing. Consider scaling your system by applying larger workloads and adding more data and queries. 

Recommendation: Perform continuous scaling testing to ensure the system can handle the load even as the data volume increases. 

Repeated testing 

Despite the expected behavior of the API, it is worth performing repeated tests. Even with the same parameters and requests, minor deviations can occur. Repeated tests help identify possible deviations, find their causes, and ensure stable operation.

Recommendation: Performing repeated tests for each configuration and request, allowing you to increase the accuracy of the test results and identify potential problems.

Selection of API testing tools

When choosing testing tools, consider modern capabilities, community support, and documentation.

Recommendation: Consider integrating the selected tools with the existing infrastructure and CI/CD pipeline.

Resistance to API changes

When writing automated tests, use structured and clean code. This will make it easier to change the tests when the API changes.

Recommendation: It is recommended to use design patterns such as Page Objects or Screenplay to increase the resistance of tests to changes in the API.

The overall success of API testing lies in combining these best practices. 

Top API Testing Tools and Framework

API testing shows some similarities with other types of testing, but it requires the use of specialized tools designed specifically for its automation. Among other aspects, these tools differ in the programming language used. QA professionals often choose between using off-the-shelf solutions or building a custom framework using its components when using an API testing tool. 

Postman API Testing: REST API tests using JavaScript 

Postman is currently one of the most popular tools used for API testing. Started as a browser extension for testing APIs, today, with integrated test automation features, Postman is much more than just an HTTP client. 

You can test APIs manually with Postman, even with almost zero JavaScript knowledge. For AQAs with extensive JavaScript knowledge, Postman has a JS testing library.

Let's consider the use of tools for this in more detail.

  1. Newman Add-on Tool: Newman is a command-line tool that allows you to run collections of queries created in Postman without a GUI. You can use the ‘newman run’ command to run a collection of test queries. This allows you to automate and integrate the API testing process into automated tests or scripts.  
  2. Configuring API requests: Major API testing frameworks such as Postman or Swagger provide a user-friendly interface for creating, configuring, and sending API requests. You can define request parameters, including methods (GET, POST, PUT, DELETE), URLs, headers, parameters, request body, etc.  
  3. Monitoring request duration: In Postman, for example, you can measure the duration of each API request. After a request is made, you can check the time it was sent and the time it was received to determine how long the request took. This helps you monitor API performance and identify potential problems with server responses. 
  4. API Responses: In Postman, after executing a request, you can view the response code returned by the server (e.g., HTTP status code). This helps determine whether the request was successful or an error occurred and react accordingly. 
  5. API Testing Tasks: API testing can be included in an automated testing process where you define expected results and compare them to actual API responses. For example, you can check if the expected status code and data are returned according to your test case.  

Automated API testing generally involves setting up, sending requests, parsing responses, and checking the results. Tools such as Postman and Newman allow you to automate and simplify this process and monitor and analyze its detailed results. 

Postman benefits: The tool is praised for its ease of use and speed, features, and many integrations. It has a user-friendly interface for creating queries and reading responses, allowing you to create automated tests quickly. Postman runs on local machines so that you can control your data. You can integrate these tests into continuous integration (CI) environments using the Newman command-line tool. 

REST Assured: Java Library with Support for Requests in XML and JSON Formats  

REST Assured is a powerful Java library for developing REST API test scripts. REST Assured is ideal for functional testing of REST API services, requiring high-level programming skills to create tests.   

REST Assured benefits: Testing APIs is a daunting task in Java, and REST Assured is designed to simplify this process. With it, you don't need to waste time creating boilerplate code to test and verify complex REST responses. An open-source library and supportive community is another significant advantage. 

JMeter: A Java-Based Tool for Measuring SOAP/REST API Performance 

Apache JMeter is a reliable and time-tested tool that was originally designed for load testing. Modern Apache JMeter allows functional, regression, and stress testing for various protocols. It is a free and open-source tool with special scripting features requiring advanced programming skills. 

JMeter benefits: JMeter allows you to simulate different types of loads, providing flexibility when testing. Additional plugins extend the capabilities and allow you to customize and extend the tool. Built-in functions simplify the dynamic input of test data. Additionally, the tool caches test results and data, allowing offline replay and test results analysis. 

Requests: A handy HTTP Library on Python  

The Requests library is a powerful tool for making HTTP requests in Python. It has an open-source code created under the Apache2 license to simplify work with HTTP requests. 

Requests benefits: This HTTP library saves time and simplifies your work by fully automating HTTP request processing and connection pool management. Y You don't need to manually add query strings to the URL or hard-encode the POST data. Request is a powerful library with easy-to-understand documentation, simple syntax, and rich functions. 

Katalon Studio: Automation Tool with Built-in API Testing Mode

Katalon Studio is a solution initially designed to automate user interface testing, but it also includes an integrated environment for quickly creating and executing API tests. 

Katalon Studio’s benefits: The main advantage of Katalon Studio over other automation tools is its built-in API testing mode. Katalon Studio provides a built-in and powerful API testing mode with auto-completion, validation, and generation of code fragments; built-in answer viewer with automatic formatting; tests importing from other API testing and editing tools such as Swagger, Postman, and WSDL.

Own API Testing Automation Framework 

Developing your framework gives you more flexibility because you are not limited by the capabilities of a particular tool and its plugins. You also get more flexibility in managing your test data. However, you will need strong programming skills to develop your framework successfully.   

With limited programming knowledge, paying attention to a ready-made tool is better. Its user-friendly interface and low programming requirements will simplify the process. It's worth noting that they check only general API issues. However, on the positive side, the user community can quickly help with joint problems.  

Therefore, in the first stages, starting with a ready-made tool, for example, Postman, is recommended. Developing your framework is more complex, but it can lead to improved functionality for your testing. Deciding which path to take depends on your skill level and the project's specifics. Explore the importance of penetration testing API to ensure the security of your applications.


The process of API testing is complex and consists of many stages, which require deep theoretical knowledge and practical skills. In this article, you learned about the types and architectures of automated API testing, how to conduct API testing, and a list of recommendations for improving this process from our specialists. We hope that you will successfully apply the acquired knowledge! 

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Why is it necessary to automate API testing?

API test automation helps speed the testing process, improve accuracy, and provide quick feedback on code changes. 

How do you automate API testing without knowledge of programming?

You can use specialized tools such as Postman to automate API testing without programming knowledge. They provide a GUI for creating and executing test scenarios with minimal programming knowledge. 

What types of tests can be automated for APIs?

The following types of tests can be automated for the API: 
- Data validation testing
- Authentication and authorization testing
- Testing interaction with the database
- Testing responses and status codes
- Testing compliance with standards and specifications

What are the most commonly used tools for API automation?

The most popular API automation tools: 
- Postman
- SoapUI
- RestAssured
- JMeter
- Newman (for testing using Postman collections)
- Swagger / OpenAPI (for automatic test generation)
These tools help automate various aspects of API testing, including test creation and execution, data validation, and standards compliance.

How do I choose the right tool for API test automation?

Consider factors like your application’s technology stack, the tool's learning curve, integrations with other systems, scripting languages supported, and the overall costs involved.

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