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API testing is essential and tells developers if APIs meet expectations for functionality, security, performance, and reliability.
API stands for application programming interface. An API is a software intermediary or go-between that enables two apps to communicate with each other. For example, every time you interact on Facebook, purchase a product on Amazon, or check the news on your phone, APIs are at work.
An API operates like this: when you utilize an application on your computer or phone, the app connects to the Internet, sending your data to the server. The server downloads the information, interprets it as needed for the app, then returns a response to the phone or computer in a way that you can understand and use it.
The reason testers test APIs is to find out if the APIs meet expectations for functionality, security, performance, and reliability. API functional testing is essential because APIs are the primary interface in application logic and because testers have found that GUI tests (graphic user interface tests) are challenging to maintain and provide limited coverage, taking into consideration the recurrent changes in DevOps and Agile software and abbreviated release cycles. Companies have found that adding API testing significantly expands their application test coverage.
Testers test APIs directly, in other words, in isolation, as a component of end-to-end testing in integration testing. Outside of RESTful APIs, transactions include various endpoints, for example:
Testers test APIs that a development team produces. In addition, they test the APIs the team uses in the application, including any third-party APIs. The tests determine if the APIs return the appropriate responses in the correct format for a wide range of conceivable requests and if the APIs react appropriately in unusual or extreme inputs and to failures. Testing normally includes SOAP web services or REST APIs with XML or JSON message loads with the system sending over JMS, HTTP, HTTPS, and MQ. Other message formats testers use during tests are EDI, FIX, and SWIFT.
Typical API automated testing involves the following:
For details about the specific tests that developers use to test APIs, see the Types section below.
To ensure a pleasant and successful user experience with your software application, it’s important to test it thoroughly. This means verifying the underlying operation of the code and its interactions with other systems and services.
UI testing alone cannot guarantee that the software works as expected. API testing assesses the application’s functionality, reliability, and performance so you can have confidence that you’re delivering high-quality software.
API testing focuses on
All of these areas are critical for the correct operation of your application.
Failure to perform sufficient API testing can result in
Proactive and extensive API testing produces better software.
In order to cover all the bases, testers employ a range of tests to test APIs. Here are the main ones.
API functional testing verifies that the API performs as expected and responds appropriately to any requests that it receives.
This is another security test. Testers input a large amount of miscellaneous data (fuzz or noise) into the system to force negative behavior or program crashes. These tests stress APIs for worst-case situations.
This type of testing verifies that the app performs correctly under both peak and normal data inputs.
During this test, testers discover whether users with little API expertise can gain access to the full API including information about processes, functions, and resources.
This test relates to the API’s actual operation, focusing specifically on the outcome of when the APIs utilize the API codebase. It concentrates on one or more of these: execution errors, monitoring, error detection, resource leaks.
This testing is for API protection and confirms that the API application is safe from external threats. It includes testing the structure of access control, user rights management, validating encryption methodologies, and authorization validation.
UI testing tests the API’s user interfaces. It focuses mainly on the interface that connects with the API as opposed to the API testing itself.
This testing is essential and happens in the final steps of the development. It confirms various features and the correct behavior of the product and also efficiency.
When APIs don’t behave as expected, it leads to broken features or security risks. These are some of the most important bugs API testing can catch.
When an API takes too long to respond, even under normal conditions, it hurts user experience and delays system workflows.
APIs that return unexpected or malformed data – like missing fields or incorrect types – cause failures in downstream systems.
Weak or misconfigured authentication lets unauthorized users access restricted endpoints or perform sensitive operations.
The API behaves differently than what’s defined – for example, returning extra fields, missing required ones, or accepting invalid inputs.
When something goes wrong, the API either fails silently or returns a generic error that’s hard to debug.
Vulnerabilities like injection points, exposed credentials, or lack of input validation that can lead to attacks or data leaks.
UI testing tests the API’s user interfaces. It focuses mainly on the interface that connects with the API as opposed to the API testing itself.
This testing is essential and happens in the final steps of the development. It confirms various features and the correct behavior of the product and also efficiency.
A high level of automation provides an array of functional test scenarios that you can replicate systematically.
Use an intuitive interface to automate complicated cases over databases, microservices, the messaging layer, and so on. This includes:
Therefore, it’s essential to recognize when API changes occur and easily, quickly, and accurately update test assets to align.
The key is to develop a system that assesses changes needed for current tests and then updates them or even creates new tests. This can substantially reduce the time and effort it takes to be sure that your tests do not fail as a result of unexpected changes and that they don’t ignore new functionalities.
This allows you to create simulated test cases, which in turn allows you to view behaviors of dependent resources that you may have a hard time accessing, that you may have difficulty configuring for testing, or that are not yet available.
These resources might be web services, databases, mainframes, or third-party applications, among others. You can use web service virtualization together with OS and hardware virtualization to gain access to the required environments. Combined, this allows you to test faster, earlier, and more thoroughly.
You can apply service virtualization in two ways with regard to API testing:
APIs are highly exposed. Thus, a great potential for volatile and unpredictable traffic exists. It’s wise to use broad performance testing to determine if your API meets expectations when it encounters surging demand or erratic behavior. Here are some examples.
Service virtualization allows you to create simulated test scenarios that assist you in testing various performance environments that are normally problematic to create in a test situation. You can test conditions like timing, delay, and latency to replicate typical, peak, and slow performance in an effort to plan for a cloud burst or someone accessing the API from a remote location on another continent.
In addition, you can create various failure and error situations that testers often find hard to reproduce in the actual program – like if your APIs use Amazon Web Services, you can create a scenario that simulates a situation where AWS is offline.
You can also configure a wide range of situations in dependent systems in order to discover if your APIs deliver proper responses under non-ordinary conditions and also if they fail reasonably well.
You may replicate links to third-party applications, which can negate any risk your tests may have on services that you are not normally allowed to attack with test data or for which you are not budgeted.
APIs, unfortunately, offer a large surface attack area. To help stop attackers and major security problems, use a multi-faceted test approach. This ensures that you have written the necessary measure of security into the application. The approach includes:
As a money saver, service virtualization allows non-security experts to perform tests because they are not writing code but simply executing proven tests in a wide variety of scenarios. And service virtualization enables you to target your API’s responses to a variety of dependency security behaviors and in numerous attack situations.
While the API economy is revolutionizing business operations in many ways, there are still some concerns about its adoption. Some of them include:
Testing microservices presents unique challenges that stem from their distributed architecture and increased complexity. Here are a few examples:
For maximum results, follow these best practices when testing microservices.
Here are two examples of situations in which you would want to perform API tests.
When a person opens an app like Instagram or Twitter, the app asks her to sign in. She can do this on the app itself or via Facebook or Google.
When the user employs either of these two web sources, it’s understood that the app has an agreement with Facebook and Google, so the app can access some of the information about the user that she has previously supplied to the sources.
Testers can test the APIs that give the app the ability to access the information it needs. The tester can also test to make sure the social media app works with Facebook and Google successfully to give the user access to the app.
When a person uses a web service like Kayak or Expedia to book airline tickets, he anticipates that he’ll see cheap flights for the date he needs to fly.
The travel app has to communicate with the participating airline companies to show the traveler the best flight times and prices. APIs make this happen.
Testers can test to make sure the APIs that give the travel app the ability to communicate with the airline companies are working correctly and that the app is supplying the proper information to the user.
The testers can test to make sure the APIs that help book the flight are working as expected and verify the payment component—the tester can test the APIs that allow the app to communicate with credit card companies and properly process payments, and those APIs that keep the user’s personal and financial data safe.
