API Testing

API Testing

As part of QA testing, API testing is one of the most challenging yet important processes in software development. API testing has numerous advantages since it can be complex, and it typically relies on protocols and standards that are difficult to locate in other types of testing.

QA testers must use API testing methodology to evaluate functionality, API performance tests, and API security tests. While developers prefer to test only the core functionality they are working on, QA testers must use API testing methodology to evaluate functionality, API performance tests, and API security tests. They examine how well all of the components work together from beginning to conclusion.

Starting the API Testing

To begin an API testing process, you must first understand the scope and purpose of API testing approaches.

Before beginning any API tests, consider the following basic questions.

  • What kinds of endpoints can you put to the test?
  • When a request is successful, what are the anticipated response codes?
  • If a request is denied, what response codes should be expected?
  • What error message should be generated when a request is failed?

Once you’ve answered the following questions correctly, you can begin experimenting with other testing methods. API testing in software development should also be examined to see what conditions or variables testers can assess and whether a system works correctly and responds appropriately. This is where the use of test cases comes into play.

After that, you can perform tests and compare their expected outcomes to their actual outcomes to demonstrate the benefits of API testing.

The following response should be analyzed in your tests:

  • Reply time
  • Data quality
  • Confirmation of authorization
  • HTTP status code
  • Error codes

Benefits of API Testing

API testing has a number of advantages than GUI testing, including increased testing efficiency and the potential to release software faster with fewer testing costs. Consider the following main advantages of API testing.

Finding bugs at an early stage of software development

APIs can be tested without the need of a user interface. That is, they can run tests without having to test the entire software. This means that a developer can detect various types of issues early in API testing, before they influence the user interface.

The advantage of API testing is that companies that use QA services save time and money.

Effective use of time

One of the benefits of API testing is that it takes less time than functional GUI testing, which requires extensive polling of web page components.

Here’s a brief comparison of how much time API testing saves as compared to testing your application’s core functionality.

3,000 API tests in 50 minutes (in parallel execution) will take 3,000 GUI tests in 30 hours (in parallel execution)

Your QA UI testing team could expect similar time reductions. When compared to automated GUI tests, choosing from a variety of API testing approaches offers greater and faster test coverage. It’s because API test automation necessitates less lines of code.

Reduced testing costs

It’s a good idea to test the application’s API level functioning before undertaking GUI tests. Early mistake detection reduces the cost of manual testing while simultaneously increasing test coverage.

API testing has the advantage of test automation being faster and more accurate than GUI test automation, resulting in fewer hours and lower software testing costs.

Non-attachment to programming languages

Data is exchanged in XML or JSON forms as part of your API testing methods. This data transmission technique is independent of application language, allowing QA engineers to automate API testing with any programming language that supports these technologies, such as PHP, Ruby, Java, JavaScript, and others.

Improved test coverage

Unit tests are limited to simply functional components within a specific application, whereas an automated API test can cover a far broader variety of capabilities. This is where the vast majority of problems arise.

API tests, on the other hand, are designed to ensure that all system components function as intended. The benefit of API testing is that it helps to improve the overall quality of the application and adds to better user experiences.

Top Tools for the API Testing

When it comes to API testing, there are a variety of API testing methods and tools to choose from, depending on your testing needs, budget, and technology.

Before you perform any API tests, consider using one of the following popular API testing tools.


Postman started out as a Chrome addon. The Postman API testing tool is now available for Windows and Mac, making it a terrific option for exploratory and manual testing.

For API testing, you can use the Postman REST API testing tool to put up automated tests and troubleshoot them.

Top features

  • Tools, collections, and workspaces are all included.
  • In addition to RAML and Swagger, you can use Postman with various formats.
  • Postman’s UI makes it easy to extract data from online APIs.
  • It doesn’t rely on the command line to write Boolean tests.

Rest Assured

REST service testing has never been easier thanks to this free and open-source Java Domain-Specific Language. The responses to these inquiries can be validated and verified using this tool.

Rest-assured API testing should be used when testing RESTful services in Java. It’s a fantastic open-source platform that allows you to test REST services using Java domain-specific languages. It’s also popular for testing JSON and XML-based applications.

Top features

  • Integrates with Serenity automation framework seamlessly.
  • Users don’t have to write any code because of the pre-existing functionality.
  • It provides a variety of ways to test and verify a secure API.
  • Given/When/Then test notation is supported by the use of Fluent API, making your tests more human-readable right away.
  • No matter which API testing methods you follow, it can handle all HTTP methods and a few specific instructions, such as POST and GET.

Katalon Studio

Katalon studio allows QA professionals to automate API, online, desktop, and mobile testing. This tool makes deployment easier by combining all frameworks, ALM connections, and plugins into a single package that can be installed quickly.

Katalon studio’s primary features are its ability to mix UI and API/Web services for multiple platforms (Windows, Mac OS, and Linux).

Top features

  • API automation testing is made easier with the help of this powerful integrated development environment (IDE).
  • All REST and SOAP requests are supported.
  • Swagger, Postman, and WSDL test requests may be imported.
  • It may be run locally and remotely, with real-time analysis.
  • Simple request composition with numerous data sources thanks to data-driven (e.g. XLS, CSV).


Because this API testing tool is headless, it can be used to test SOAP and REST APIs as well as web services. As a result, testers typically select it as one of the most useful tools for asynchronous testing of complicated situations.

It’s also known for its user-friendliness and great data-driven testing.

Top features (Free package)

  • With SoapUI, you have a slew of enterprise-level capabilities. For instance, you get the MockService and its methods generated for you automatically from a WSDL that you provide.
  • SoapUI helps sophisticated test scenarios without writing any scripts with its drag & drop functionality. You can also add test suites to a project once you create it.
  • Once you conduct a load test, the LoadUI generates a report that helps assess the application’s load capacity. Use SoapUI to create complex load tests from functional API tests simply.

Pro package features

  • You can test APIs using data supplied from files, databases, and Excel, allowing them to replicate how users interact with the APIs.
  • Enables asynchronous testing and native CI/CD integrations.


The Paw tool can be used to inspect and explain APIs that you design or acquire. The app’s native macOS interface can be used to make calls, and it can test server answers, generate client passes, and introduce new APIs.

When it comes to testing and describing APIs, Paw is a one-stop shop for testing and describing APIs on the Mac. With this feature-rich and well-designed Mac program, you can create HTTP requests, evaluate the server’s response, and even write code.

Top features

  • Analyze API capability for Mac centering by delivering all forms of HTTPS requests to API.
  • Use JSON Schema to identify and clarify the type of API tester being used.
  • Connection buttons are enabled without compromising the user’s capacity to collaborate.
  • Using API, users can find leggings and then using Paw, a network of users can work together to make improvements.

Types of API testing

APIs have come a long way from their humble beginnings as simple libraries of code that programs could use to interact on the same system to the more complex remote APIs that allow programs on one computer to interact with programs on another.

There are numerous specialty tests, and no list could ever include them all, but these are the seven most common types of API testing that the QA team may use.

Unit testing

The term “unit testing” refers to the process of writing API tests that are executed with each new version of an application. They should be written close to the code in order to pass a build of the program.

The amount of code coverage an API requires is determined by its risk level and the functions it delivers.

It’s crucial to think about this API testing area because it’ll help with the rest of the job in the future.

Integration testing

To stay ahead of the game, effective API integration testing is required. API integration testing is necessary to guarantee that the functionality of your product is not jeopardized.

The user experience is mostly determined by the app’s functionality. The success or failure of your product is determined by how the user feels about it.

As a result of its scope, structure, and ongoing evolution, API integration tests are complex and controversial. The advantages, on the other hand, include speedier manufacture of higher-quality goods, making it a difficult task to take on.

Performance testing

The purpose of this API performance test is to look at the program’s response time, dependability, speed, and functionality. As a result, optimal efficiency is ensured. Rather than faults, this test tries to alleviate software performance bottlenecks.

Load testing

This is a non-functional test that aids in determining a software application’s or product’s performance. In software development, end-to-end API testing is published in a real-time environment where multiple users can test it at the same time.

Load testing aids the developer in determining the program’s running capabilities, determining the app’s viability while several users are using it, and determining the app’s ability to scale to accommodate more users.

Runtime error detection

This is a strong way to keep track of and supervise a program that use bug-hunting techniques like human or automated testing. Exceptions, resource leaks, and so on are all examples of this.

If carried out with the utmost care, the test may yield reliable results in terms of bug detection. You can concentrate on specific features such as monitoring, error detection, execution problems, and any potential leaks; these tests will give you the highest chance of finding serious flaws.

Security testing

This test ensures that API testing in software development, as well as implementation, is safe from external threats.

API security testing also includes procedures such as validation of encryption mechanisms and the design of API access control. It also manages user permissions and checks authorizations.

Validation testing

Validation testing is one of the most important tests carried out at the end of the product development process. It looks at the product, the way people act, and the overall efficiency.

Validation testing may be considered an assurance that the API app is being constructed correctly when it comes to API app development.

How to do API Testing?

Without the use of a user interface, APIs (application programming interfaces) are tested at the message layer. The QA team uses API testing to see if APIs meet their expectations in terms of functionality, dependability, speed, and security when they first start it.

The following methods for starting API testing should be included in your product architecture API testing.

Gathering API requirements

Before testing, it’s vital to obtain the API’s requirements. Depending on where and how an API fits into the entire application process, you can utilize API to API comparison or database verification to assess input and output data.

Discovery Testing

API discovery is required for API integration and API performance testing. When it comes to API discovery, QA engineers must hunt out even the tiniest of details to ensure that everything functions properly.

You should work out the best strategy to get to API testing in the first place at this level of API discovery.

API noise in various apps, software, and websites can be reduced and eliminated by using the correct API testing approach. The discovery process necessitates human execution of API calls in order to verify API calls established in R&D and client requirements.

Define the API requirements

It’s difficult to write good requirements. As a result, open communication is required to define correct requirements, as every stakeholder can contribute useful information. They may also pose some difficult questions that must be answered.

This is why collaboration is so important – developers, testers, system architects, analysts, and product owners are all experts in their fields and should be included in the development of requirements.

To do so, a well-coordinated brainstorming session is required to address essential questions such as;

  • How are you going to use this API?
  • What are the ways through which the application can handle data?
  • How to handle system failure?
  • How can the system handle output?
  • What are the options for the system to handle unexpected input?
  • What fields does the API transmit and receive?
  • How will the API communicate with other APIs, including the protocol to be used?
  • Criteria for admission and exit.
  • The API/pass/fail feature’s criterion.

Data Input → Output → Outcome Validation and Verification

Each of these tasks is relatively simple when compared to managing the large amount of test data that must be created and confirmed. Methods for verifying test data can be difficult, and they can make or break the testing process for an API or service. API testing automation may be useful in this situation.

Next steps

  • Next, you need to create a testing environment that’s as close to real-world conditions as feasible.
  • Ensure including documentation review; this is also known as static API testing since we are evaluating documentation that will never be performed.
  • Use one API request as a proof of concept before diving into it and making sure all your scripts are functional.
  • Carry fuzz testing and all other functional testing that includes briefing on which tests will be conducted at what level. This is the step to plan all your tests.
  • In order to speed up testing, you can create stubs and drivers in advance of the whole environment’s integration.
  • End-to-end testing requires API integration with the whole environment and running the test cases.
  • Do not fail to check whether the outcomes of your test executions fit the specifications. A single test case failing does not always suggest that the whole feature should be rejected for release. But it means that a thorough investigation of the underlying causes is required by way of conducting a risk assessment.
  • Make any necessary fixes and retest all of the features that have failed.
  • User Acceptance Testing (UAT) should begin only when all the criteria are met.
  • If needed, perform any fixes and retest the feature that failed.
  • Once the test documentation is complete and the criteria are met, the QA lead will approve the feature and will allow it to be implemented live.
  • Also, it is recommended to run a sanity check prior to releasing the final version.
  • Check any logs you have or prospective service desk instances to see if there are any issues with your production releases.


When it comes to certifying software or an application, API testing is becoming a difficult concept in the software and QA testing chain. If you’re having trouble getting ensured execution, contact Nile Bits QA experts.

We are constantly working to improve our platform and procedures in order to take the testing experience to a whole new level and increase client satisfaction.

Nile Bits offers a variety of testing services both as part of our full-service mobile app development and as a stand-alone service. Test case-based testing is performed by our skilled QA team.

It establishes a baseline that uses a multi-execution channel technique to obtain true pass/fail outcomes through AI Automation, manual testing, and crowdsourcing.

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