API Testing Automation: How And Why Automate API Testing

But while APIs usually serve a single purpose and are not particularly large or complex software products, it takes a lot of testing on the developers’ side to ensure the spotless performance, complete functionality, and strong security of an API. And many organizations now prefer to automate API testing to save time and money on QA and get more consistent results. In today’s guide, we are going to talk about why and how to use API automation testing in your company.

What Is API Testing & How Is It Different From Other Types of Testing?

API testing is the process of verifying the correct operation of an API (Application Programming Interface) by interacting directly with the application, bypassing the user interface. As more and more businesses rely on API technology to offer more robust functionality to their users and surpass the competition, API testing becomes a mainstay of any current software development and QA project.

API testing is also an important part of the switch from the monolith architecture to microservices. A growing number of companies prefer to build flexible and scalable solutions consisting of multiple smaller units such as APIs instead of large, monolithic systems. On the one hand, this leads to the development of handy software solutions with a specific purpose. On the other hand, it creates the need to test each unit or API separately and in combination with other units.

What Are The Key Benefits of API Test Automation?

As with many other types and levels of software testing, it’s possible to do API testing entirely manually. However, automating the process brings some sizable benefits to the whole software development and QA operation. Here are a few reasons why API testing is important and deserves your utmost attention:

• Automating API testing allows you to catch bugs earlier, before they do more damage to the entire product or stall the development process.
• Automated API testing provides nearly endless test case reusability opportunities, resulting in more efficient testing and API products being developed faster.
• API test automation eliminates the risk of human error skewering the results of testing, misinterpreting the results, or skipping some essential steps in the testing process.
• While automating API tests requires financial investment in the initial stages, test case reusability allows the organization to save money on testing in the long run.
• API testing automation improves the performance, security, and scalability of a software solution that uses API technology more noticeably than manual testing.

The Role of API Testing Automation in API-First Development

A relatively new trend among software development companies and businesses developing their own software is the API-first approach. Under this approach, development teams build software applications by linking together several different APIs. This is a product-centric framework that puts emphasis on the functionality brought by external services through APIs. And with teams often racing against the clock to unveil better products faster than their competitors, continuous and effective API testing, especially API testing automation, can significantly improve the QA process and lead to higher quality software that is released according to schedule.

How API Test Automation Helps with Shift-Left Testing

API test automation helps teams shift left by enabling earlier and more frequent testing during the software development lifecycle. Traditionally, testing is done after development is complete, but with automation, tests can be integrated early into the process, right alongside code development.

Automated API tests can run continuously as code is written, providing immediate feedback to developers. This early detection of defects allows teams to identify and fix issues before they become complex and costly to resolve. Automation supports Continuous Integration (CI) pipelines, allowing tests to run every time new code is committed, ensuring that any breaking changes are caught early.

Additionally, API automation reduces the manual testing effort, freeing testers to focus on more complex tasks or exploratory testing. It also promotes collaboration between developers and testers, as both can work together to create and maintain automated tests.

In short, API test automation streamlines testing processes, speeds up feedback, and helps teams deliver more stable, high-quality software while reducing overall development time and costs.

Is It Always a Good Idea to Automate API Testing?

The benefits of API automation testing seem far too vast for anyone to doubt the usefulness of this QA technique. But does it always make sense to automate API testing within an organization?

From a practical standpoint, automation is typically not needed on small testing projects that are not expected to be long-term. Automation API testing may also be redundant when there isn’t a substantial regression test suite to take care of, as automation techniques work perfectly with regression testing.

The situation where automating API testing makes perfect sense and is definitely needed is when the API is the product that is being developed, as opposed to being just another component of a bigger product. With the reputation of the company riding on the quality of the API, rigorous testing, including automated QA, is a must.

Types of API Automation Testing

The goal of API testing automation is to test the API at every level and to make sure it’s prepared to be used by its end customers. This is why it’s possible to break down the overall process of API automation testing into specific types of tests that are designed to check different areas of the product. These are the most commonly used types of API automated testing.

1. Functional Testing

As one of the most vital types of API testing, functional testing is responsible for verifying the correct operation of the API’s principal functions. In other words, this type of testing is performed to make sure that the API is doing everything it was originally intended to do.

2. UI Testing

While UI testing does not directly deal with testing the API itself, it performs another important function in the API testing process by investigating all the ways the API is tied into the user interface of the application and vice versa.

3. Validation Testing

Validation testing typically happens at the last stages of the API development process. It is meant to verify various aspects of the product, including correct operation and presence of all design elements. A successfully passed validation test means the product is ready for release.

4. Load Testing

Since APIs are often designed to work with large amounts of data and under different circumstances, load testing is vital for making sure that the API can handle both normal and peak numbers of requests.

5. Security Testing

Often dealing with sensitive company or customer data, APIs can undoubtedly benefit from security testing. This can also include penetration testing as a subset of security testing, while automation can further streamline the process and make it more efficient.

Who Can Do API Automation Testing? What Skills and Competencies Are Required?

The common opinion in the testing community is that API testing automation is not the most complex type or level of testing. This is why this process does not strictly require a senior automation QA or a lead to be involved. 

Still, a certain set of skills can make the adoption of API automation testing practices easier and the project results more predictable and dependable. Here are the skills and competencies an engineer needs for automating API testing:

• Strong manual testing knowledge, which enables the engineer to approach testing with maximum precision and add value through manual testing where automation is not applicable.
• Knowledge of programming languages, or at least one, which can be useful both for understanding the inner workings of the product being tested and for creating custom frameworks and test scripts.
• Ability to understand business requirements as well as technical ones — in other words, the API automation testing engineer should be able to see beyond the failed or passed tests and actually know how their efforts impact the business side of the product.
• Familiarity with automation tools — not necessarily a lot of them, but with at least one or two popular tools nonetheless. Selenium, Postman, and JMeter are a good place to start.
• Awareness of different development models, which can influence the way the team approaches API testing automation, how much time they have for each step, how often the stakeholders will expect reports, and so on.

How to Develop an Effective API Automation Testing Strategy

An integral step of automating API testing is developing a strategy for the upcoming QA project. With a good strategy, you can plan your resources wisely, ensure all-encompassing testing coverage, and make the team’s testing efforts as efficient as possible. Here is how to build an API automation strategy that works perfectly for your organization.

1. Collaborate with Manual Testers

Ideally, an API testing automation project is a collaborative effort between the manual and the automated QA departments. It is usually possible to launch an API automation testing project with the automation team alone. Still, the results are always going to be better when there are already some test cases written by the manual testers for the automation QAs to build their work upon.

2. Communicate with the Developers

Another vital aspect of a successful API automation testing project is regular communication between the QAs and the developers behind the product. This can be especially useful when there isn’t enough documentation on the project, or it’s lacking in quality. The developers can identify the endpoints and key features of the application, among other things.

3. Prioritize the Test Cases

Automating every single API test case is both impractical and not always realistic. This is why there needs to be a person with significant API testing experience who is able to correctly prioritize the test cases. For example, when the app being tested includes third-party APIs, there is no need to test those APIs themselves  — only the way they interact with the main app.

4. Consider Local Laws and Regulations

One of the often overlooked aspects of API testing automation is not the technical parameters of the application, but its compliance with local regulations. This is particularly essential for products intended for international use. Laws and regulations can concern data storage, privacy, age limits, and so on, and they all need to be taken into account while testing.

5. Examine Every Possible Scenario

Since the primary purpose of API automation testing is in-depth quality assurance of a product that countless users will depend on, it’s important to consider every single scenario when developing a testing strategy. For example, how the app is going to behave when a third-party API stops working, or an in-house API is down for scheduled maintenance?

6. Pay Attention to the Revenue Streams

Some of the most important parts of an application that uses APIs are often the parts that directly impact the company’s revenue. For an eCommerce store, it can be the payment gateway application, while for a flight booking platform, it can be a feature that offers discounted ticket + hotel + car rental bundles. This type of functionality needs to be tested with special precision.

7. Put Emphasis on Regression Testing

While it’s true for many types of products and testing levels, regression testing is paramount for API automation testing. There are few things more harmful to the reputation of a product and company overall than a particular feature failing to work properly or being dropped altogether after the customers have gotten used to it. This is why regression testing should never be skipped in automating API testing.

How to Automate API Testing

Any successful API testing automation project is thoroughly planned and follows a specific set of steps designed by the automation team. Here are the steps a typical project in API testing automation includes.

1. Create a Detailed Plan

This is a crucial step on a way to automating your API testing efforts. A well-designed plan will help you understand the work ahead better and prepare your team members for the subsequent steps you will all need to take. Planning the project also helps you get a firm grasp of the available resources, which allows you to keep the project budget under control later.

2. Identify the Requirements

A comprehensive list of requirements gives a sense of direction to an API automation testing project and helps the team keep their eyes on the key goals of the project. The requirements will always depend on the project specifics, but the most typical ones include:

• Who the API is for and what it’s meant to do
• Principal and secondary functionality of the API
• Whether and how it interacts with other APIs
• What the team is looking for with testing
• The definition of passed and failed tests

3. Prepare the Test Cases

Whether you already have a roster of API test cases written by the manual team or you are planning to write the cases from scratch and have it done by the automation team, the number and variety of test cases have a direct impact on the process and the results of the project. Two popular approaches for designing test cases include behavior-driven and data-driven testing.

4. Select the Tools and the Framework

A testing framework is required to standardize the work of the QA team and improve the quality of testing overall. Teams may choose from ready-made frameworks or design their own, although the latter takes senior-level skills and experience. As for the tools, the choice is usually between paid and open-source ones, and there are plenty of options available in both categories.

5. Set Up the Testing Environment

This is the part of the project that should ideally be entrusted to the DevOps team or engineers with similar competencies. Setting up the testing environment for an API testing automation project includes configuring servers, databases, and other architecture items the API is going to interact with.

6. Execute the Tests and Analyze the Results

This is the stage where you get to evaluate not only the quality and stability of the API, but also the success of the previous steps of project planning. To increase the efficiency of testing and reduce dependencies, you can opt for parallel test running. As for analyzing the results of testing, you can rely on one or more API automation testing tools.

Common Test Cases for API Testing Automation

When automating testing of an API solution, there are many things to take into consideration: the functionality, UI, performance, security, and stability of the application depend on how well it’s tested. The exact selection of test cases depends on the project goals and software specifics, but this list is a good starting point:

• Verify API response status codes (e.g., 200, 404, 500).
• Validate correct data in the response body.
• Test response structure and schema validation (JSON, XML).
• Test CRUD operations (Create, Read, Update, Delete).
• Ensure unauthorized requests return appropriate errors (401, 403).
• Check invalid data formats and missing required fields.
• Test how the API handles incorrect HTTP methods.
• Measure response time and performance.
• Simulate load testing with multiple users.
• Test security against SQL injection and XSS vulnerabilities.
• Validate data integrity and consistency across endpoints.
• Test pagination, sorting, and filtering functionality.
• Ensure proper enforcement of rate limiting and throttling.
• Verify file upload and download capabilities.
• Test session/token expiration and proper handling of expired credentials.

How to Choose an API Testing Tools + 5 Popular Tools for API Automated Testing

A test automation framework and set of tools can influence the outcome of the project more than some realize. These days, there is no shortage of tools and frameworks for automating API testing: there is a perfect solution for every project, development model, team size, and budget. Plus, new tools appear every year and never fail to attract the attention of QA engineers. Here are the top five tools to help you automate API testing.

Knowing the most popular tools for API testing automation is a great way to round up some options for your upcoming project. However, automating API testing using the most popular tools isn’t always the most practical decision, as the specifics and needs of the project can be too unique for that. Here are a few practical tips for choosing the right tool for automation API testing:

1. Identify project requirements. Determine the key requirements, such as the type of APIs (REST, SOAP, GraphQL), supported data formats (JSON, XML), and test cases (functional, performance, security).
2. Evaluate team skills. Assess the team’s expertise in specific programming languages or tools. Choose a tool that aligns with their skillset to avoid steep learning curves.
3. Check for integration with CI/CD pipelines. Ensure the tool integrates seamlessly with your CI/CD pipeline to support continuous testing and automation workflows.
4. Consider ease of use. Prioritize tools that offer a user-friendly interface, detailed documentation, and simple setup to streamline the automation process.
5. Look for comprehensive reporting. Choose a tool that provides clear and detailed reporting with test result logs, error tracking, and performance metrics for easy analysis.
6. Support for data-driven testing. Verify that the tool allows running tests with various input data sets, which is essential for covering different scenarios and edge cases.
7. Ensure support for mocking. Select a tool that offers mocking or stubbing capabilities, enabling you to simulate API dependencies or third-party services during testing.
8. Check for scalability. Ensure the tool can scale with the project’s needs, including the ability to handle a growing number of tests, endpoints, and users over time.
9. Evaluate cross-platform and environment support. The tool should work across different environments (local, cloud) and support various platforms (Windows, Linux, macOS).
10. Review cost and licensing. Consider your project budget and evaluate free, open-source tools versus paid solutions based on the tool’s features and long-term benefits.
11. Analyze community support and updates. Choose a tool with active community support, regular updates, and responsive customer service for resolving issues quickly.
12. Start with a trial. Run a pilot project or trial version of the tool to ensure it meets your project’s needs, supports your testing goals, and integrates with your existing workflows.

Metrics and KPIs to Use in API Automated Testing

There are many ways to measure the efficiency of automation testing and its effect on the overall state of the application. However, few are as effective as metrics and KPIs. Here are the ones that are best suited for automated testing of APIs.

1. Test Coverage — measures the percentage of API endpoints, methods, or business scenarios covered by automated tests. High coverage indicates that most of the functionality is tested, reducing the risk of defects.
2. Pass/Fail Rate — tracks the number of tests that pass versus those that fail in each test cycle. A low pass rate may indicate issues with the API or the tests themselves.
3. Defect Detection Rate — measures the number of defects found during testing compared to those found after release. High detection in early stages reflects effective testing.
4. Test Execution Time — tracks how long it takes for the test suite to run. Optimizing execution time is crucial in continuous integration environments.
5. Automation Coverage — measures the percentage of API test cases that are automated versus manual. Higher automation coverage implies better efficiency and faster feedback loops.
6. Mean Time to Detection (MTTD) — tracks the average time taken to detect defects after code is committed. Lower MTTD means faster issue identification.
7. Mean Time to Resolution (MTTR) — measures the average time taken to resolve defects found through testing. Short MTTR shows efficiency in addressing issues.

Strategies and Best Practices for API Testing Automation

Automated API testing helps release high-quality, reliable products right on time. However, it is only possible to reap all the benefits that testing offers when the process is designed the right way. Here are the most effective strategies and best practices to implement in your process of API testing automation.

1. Design Test Cases Early

Start by designing API test cases as early as possible in the development lifecycle. This aligns with the “shift-left” testing approach, where testing begins alongside or soon after development starts. Early design helps identify potential issues in the API specification and ensures thorough coverage.

2. Use Data-Driven Testing

Data-driven testing involves running the same test case multiple times with different sets of input data. This approach is especially beneficial for APIs that accept multiple parameters. By separating the test logic from the data, you can easily expand your test coverage without rewriting test scripts.

3. Prioritize Critical APIs and High-Risk Areas

Not all APIs need the same level of testing. Prioritize automating tests for critical APIs and those that have complex logic or high usage. Focus on endpoints that are likely to have a significant impact on users or the system if they fail, and on areas of the API where bugs have historically occurred.

4. Implement Continuous Integration

Integrate API tests into your CI/CD pipeline. This ensures that API tests are automatically triggered whenever code is pushed, providing immediate feedback to developers. Continuous testing also helps maintain API stability by catching issues early in the development cycle.

5. Use Mocking for Dependencies

When APIs depend on external services or systems, use mocks or stubs to simulate those dependencies during testing. This allows you to test API behavior in isolation, without relying on the availability or behavior of third-party systems. It also enables testing of various scenarios, such as how the API behaves when an external service is slow or returns errors.

6. Leverage Test Automation Tools

Use robust API testing tools like Postman, SoapUI, or REST-assured. These tools provide features like automated test execution, environment management, reporting, and CI/CD integration. Choose a tool that fits your tech stack and team expertise, and ensure it supports features like assertions, test data generation, and mocking.

7. Focus on Stability and Maintainability

Ensure your automated tests are stable and easy to maintain. Write modular, reusable, and well-documented test scripts so that they can be easily updated as the API evolves. This includes properly handling dynamic elements such as timestamps, authorization tokens, or unique IDs.

8. Automate Regression Testing

Make sure your API automation covers regression testing. Automated regression tests ensure that new code changes do not break existing functionality. Run these tests frequently to maintain confidence in the stability of the API.

9. Incorporate Performance and Load Testing

In addition to functional testing, automate performance and load tests to assess how your API performs under different levels of stress. Tools like JMeter or Gatling can simulate multiple users and high traffic loads, helping you identify performance bottlenecks or scalability issues early.

10. Monitor and Analyze Test Results

Set up automated reporting and monitoring for your API tests. Analyze test results to identify trends, recurring failures, or performance issues. Most automation tools offer dashboards or integration with reporting tools to help teams review and act on test outcomes quickly.

11. Establish Cross-Team Collaboration

Ensure that API test automation is a collaborative effort between developers, testers, and DevOps teams. Developers can contribute by writing unit tests for individual API methods, while testers focus on integration and system-level testing. Cross-functional collaboration improves test quality and coverage.

12. Use Version Control for Test Scripts

Keep your automated test scripts in version control systems like Git. This allows you to track changes, collaborate effectively, and maintain consistency with the development codebase. It also helps rollback to previous versions if needed.

Key Challenges of API Automation Testing

Even when it seems like everything was done right in preparation for automating API testing, there are still a few issues to be aware of as a QA engineer or project stakeholder. They won’t necessarily occur on every project, but being prepared for possible challenges is half the battle. These are the challenges that API testing automation teams encounter most frequently.

1. Choice of Framework and Tools

It’s not always easy to pick the right framework and tools for an API automation testing project, especially if the team is doing it for the first time. Organizations are often inclined to use open-source tools, which may not meet all of the project needs, and it goes without saying that it takes an experienced automation engineer, preferably a lead, to choose or design the perfect framework.

2. Lack of Employee Buy-In

The employees within an organization can be reluctant to start an API automation testing project for different reasons. The management team can be worried about the project cost and the need to hire new employees specifically for the project. The QA team, in turn, can be concerned about the complexity of the project and whether they have the skills required to launch the project successfully.

3. Proper Call Sequencing

APIs often depend on a specific order of calls to function properly, which is not always easily attainable in the process of testing automation. And if calls are not made in the right order, the team may end up with far more failed tests than they intended. This is an especially frequent problem with multi-threaded APIs, where the call order can get even more complicated.

4. Endless Range of Integrations and Combinations

There aren’t many software products out there that use just one API. And any new API or software unit can disrupt the performance of the API being tested. The more APIs the product uses, the more possible integration combinations there can be. The sheer number of those combinations can become an additional challenge for a QA team with limited resources.

5. Resource and Budget Concerns

While API testing automation is not as resource-intensive as some other types and levels of testing, it can nonetheless be rather expensive to set up an automation testing operation from scratch. One of the solutions for this challenge can be using outside help — for example, outsourcing part of your testing needs to a reliable QA partner.

Final Thoughts

For organizations developing APIs or actively incorporating APIs into their software solutions, automating API testing is not just one of the options to consider — it’s how they can ensure that their product is ready to be released and will not disappoint the customers with its performance, security, or functionality. We hope the tips and insights above will help you successfully plan and launch an API testing automation project.