What Is API Testing?

APIs have become the center of software development, connecting and transfering data and logic across dispirate systems and applications. Luckily, testing them can greatly improve the efficiency of your testing strategy as a whole, helping you deliver software faster than ever.

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APIs, or Application Programming Interfaces, are the connecting tissue between different systems or layers of an application. Applications often have three layers: a data layer, a service (API) layer, and a presentation (UI) layer. The API layer contains the business logic of an application - the rules of how users can interact with services, data, or functions of the app.  Because the API or service layer directly touches both the data layer and the presentation layer, it presents the sweet spot of continous testing for QA and Development teams. While traditional testing has been focused on the UI, the advantages of API testing are becoming well known.

While there are many aspects of API testing, it generally consists of make requests to a single or sometimes multiple API endpoints and validate the response - whether for performance, security, functional correctness, or just a status check. While UI testing may focus on validating the look and feel of a web interface or that a particular payment button works - API testing puts much more emphasis on the testing of business logic, data responses and security, and performance bottlenecks.

The Benefits of API Testing

Earlier Testing -

With API testing, once the logic is designed, tests can be built to validate the correctness in responses and data. We don't have to wait for various teams to finish their work or for full applications to be built - test cases are isolated and ready to built immediately.

Easier Test Maintenance -

UIs are constantly changing and moving around based on how they are accessed - browsers, devices, screen orientation, etc. This creates a nightmare scenario where tests are being constantly rewritten to keep up with the actual code in production. API changes are much more controlled and infrequent - often times API definitions files like OpenAPI Spec can help make refactoring tests only a seconds of work.

Faster Time To Resolution -

When API tests fail, we know exactly where our system broke and where the defect can be found. This helps reduce time triaging bugs between builds, integrations, and even different team-members. The small, isolated footprint of an API test is perfect for faster MTTR stats, a valuable KPI for DevOps teams.

Speed and Coverage of Testing -

300 UI tests may take 30 hours to run. 300 API tests could be run in 3 minutes. That means you’ll find more bugs in less time, while also being about to fix them immediately.

An Example:

The below example is a fairly simple and common functional test occuring at the UI level. We're heading to a website, filling out a form, submitting the form, and verifying that we are brought to the next screen. 

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At the UI level, this simple test can present us with a couple of challenges. First, we are hampered by the physical limits of our browser and network connection, having to load the browser each time we want to run an interation of this test. Second, any of these elements could change on the screen and our test would fail - if the "Dogs" entry is covering the "Cat" entry, we wouldn't be able to click it and our tests would fail. These challenges are annoying on their own - now try driving 10,000 different names and combinations through this form and see your build time grind to a halt. 

With API Testing, this entire testing scenario can, and should, be boiled down to one step:

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The Types of API Testing:

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Unit Testing

While the testing world can be filled with misnomers, the easiest way to think about a "unit test" and APIs is testing a single endpoint, with a single request, looking for a single response or set of responses. Many times, this type of testing can be done manually via the command line and something like a cURL command or with lightweight tools like SoapUI.

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Integration Testing

Integration testing is the most often used form of API testing, as APIs are at the center of most integrations between internal or third-party services 

End-to-End Testing

End-to-End testing can help us validate the flow of data and information between a few different API connections. 

Performance Testing

We are trying to change the paradigm of Load testing and shift it left into every commit. Previously, load testing was kept in the hands of the few and was difficult to execute in a CI/CD environment. LoadUI Pro is a performance testing tool for RESTful, SOAP, and other web services that enables nearly any team member to embed performance tests into their CI/CD pipeline.

Why SmartBear for API Testing?

Ease of Test Creation
SmartBear provides automation tools and frameworks for developers and testers to help validate and verify UIs, APIs, and databases. 
Automate in Your CI/CD
Each of our test automation tools comes with out of the box plugins with popular CI servers like Jenkins and a CLI for others.
Cost Savings
See instant ROI and savings with easy-to-use tools that you can trial and implement before buying.
Better Test Coverage
Run tests at scale with real-world data on virtualized infrastructure, real browsers, or with generated load.
Broad Language Support
Don't spend time learning proprietary languages - our tools work out of the box with your favorite languages like Python, JavaScript, and more.
Faster Debugging
Run automated tests in a continuous pipeline giving your team faster feedback, reducing debugging time and time to resolution.