Why API testing is critical for today’s business applications

By Yasmin Duggal / 14th Jul 2021

What is API testing?

An application programming interface (API) enables communication and data exchange between two separate software systems.  The application (or service) layer sits between the presentation and database layers and lays out the rules of how users can interact with services, data or functions of the application. API testing is a software testing practice that tests the functionality, reliability, performance and security of an API. It generally involves making requests to a single or sometimes multiple API endpoints and validating the response.

This post explores the benefits of API performance testing, the difference between manual testing and API testing automation, and how your business can start API testing.

Where is API testing performed?

API testing is performed at the service layer – in between the presentation and database layers – where business logic processing is carried out. This is where all transactions between the user interface and database layers take place.

Benefits of API testing

Testing APIs can greatly improve the efficiency of your testing strategy, helping you deliver software faster than ever. The key benefits of API performance testing include:

  • Easier test maintenance: API testing is much more controlled and infrequent than GUI (graphical user-interface) testing.
  • Faster time to resolution: It’s common that executing API testing saves up to eight hours compared to GUI testing, allowing software dev teams to release products faster.
  • Improved test coverage: API testing allows you to create automated tests with high coverage, including functional testing and non-functional testing.
  • Language independent: Data is exchanged via XML and JSON formats, so any language can be used for test automation. Built-in libraries support comparing data using these formats.

Types of API testing

  • Functionality testing: Essentially making sure the API does everything it’s supposed to do.
  • Validation testing: This makes sure the API can be consistently connected to and lead to consistent results. In other words, validation or reliability testing can be seen as an assurance of the correct development.
  • Security testing: This practice ensures the API implementation is secure from external threats. It includes what type of authentication is required and whether sensitive data is encrypted over HTTP or both.
  • Load testing: This checks the app’s performance in both normal and peak conditions by ensuring an API can handle an expected traffic load, meaning businesses can identify potential bottlenecks.
  • Runtime and error detection: This tests monitoring, execution errors, resource leaks, or error detection – and basically checks for every kind of wrong input the user can possibly supply.
  • Documentation testing: Also called discovery testing, the test team has to ensure that the API documentation easily guides the user enough to interact with the API.

Manual testing vs. automated testing

In a nutshell, manual API testing is done by a human tester (QA analyst) without the help of any automated software tools, and automated API testing is done via code or test scripts.

Manual API testing discovers bugs in the software under development. The tester checks the essential features, executes test cases and generates test reports.

API testing automation involves testers writing code or test scripts to automate test execution, using automation tools to validate the software.

The main difference between the two testing types is that automated testing allows you to execute repetitive tasks and regression test without the intervention of a human tester, although it does require some manual effort to create the testing scripts.

Pros and cons of manual API testing

Pros

  • Get fast and accurate visual feedback
  • Less expensive as you don’t need to spend your budget for the automation tools and process
  • Possible without programming knowledge
  • Allows random testing

Cons

  • The manual testing process can’t be recorded, so it is not possible to reuse the manual test.
  • Certain tasks are difficult to perform manually which may require an additional time of the software testing phase
  • Inherently less accurate due to the risk of human error
  • Time consuming

Pros and cons of automated API testing

Pros

  • Much more reliable than manual testing as it is code and script based and removes the risk of human error
  • Fast and accurate process
  • Helps you to find more bugs compare to a human tester
  • Process can be recorded which allows you to reuse and execute the same kind of testing operations
  • Supports various applications
  • Testing coverage can be increased as the automation testing tool never forgets to check even the smallest unit

Cons

  • Difficult to get insight into visual aspects of your UI like colors, font, sizes, contrast or button sizes without human interaction
  • Testing tools can be expensive
  • Every automation tool has its limitations which reduces the scope of automation
  • Test maintenance is costly and debugging the test script is a major issue in the automated testing process

How to start API testing

The first part of API performance testing involves setting up a testing environment, with the required set of parameters around the API. This involves configuring the database and server for the application’s requirements.

Next, make an API call to make sure nothing is broken before you start more testing.

Start combining your application data with your API tests to ensure that the API performs as expected against possible known input configurations.

Decide what your testing boundaries and desired outcomes from the test should be, by asking:

  • Who is your API consumer?
  • What environment/s should the API typically be used?
  • What aspects of the API are you testing?
  • What problems are we testing for?
  • What are your priorities to test?
  • What could happen in normal / abnormal circumstances?
  • How will you measure success?
  • What other APIs could this API potentially interact with?
  • Who oversees testing which aspect?

Challenges of API testing

While API testing practices help QA and development teams create code that works most efficiently, they face several unique challenges when testing APIs. Whether manually testing or using API testing automation, the most common challenges include:

Testing and validating parameter combinations

Parameter selection and categorization is required has to be known to the testers, but the number of parameters and use cases for those parameters can be overwhelming. It’s necessary to test all possible parameter request combinations in the API to test for problems pertaining to specific configurations, and the team must make sure all parameter data fits the correct numerical data type, e.g., US phone numbers appearing in a 10-digit format.

Sequencing the API calls

Often API calls need to appear in a specific to work, which becomes increasingly difficult when working with more complication, multi-threaded applications that use call-back features and maps, for instance.

Tracking system integration

Making sure the API testing system is working correctly with the data tracking system is necessary to bring back accurate responses on whether an API call is working. It’s also used to passively monitor API performance but offers a critical challenge to testers.

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API testing is an essential part of development for today’s business applications, and ensuring your APIs are secure is one critical element of that process.

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