A guide to successful API testing

April 11, 2023

Elea Andrea Almazora

To make sure your APIs are working properly, they need to go through continuous and thorough testing.

But what’s API testing? And how should you carry it out?

We’ll take you through what this type of testing entails, the different tests you can perform, the best practices you can adopt, and the benefits that testing ultimately provides.

But to get us started, and to make that we’re on the same page, let’s review what an API is.

What is an API?

An API is part of any server that receives requests and sends responses. It essentially allows separate programs to communicate with each other.

For example, if you use WFO software (workforce optimization software), it needs to be able to communicate with your organization’s main interface. APIs are behind this communication. It is the ‘middleman’ between the layers and systems in an application or piece of software.

APIs define requests that can be made, acceptable data formats, and how to make requests. There are two broad classes of web service for Web API. This consists of SOAP (Simple Object Access Protocol) and REST (Representational State Transfer).

SOAP: A standard protocol defined by W3C standards for sending and receiving web service requests and responses.
REST: A web standards-based architecture that uses HTTP and does not have an official standard.

Related: What is a REST API?

What is API testing?

Now that we understand what an API is and what it does, let’s move on to API testing.

At its core, API testing is the process of evaluating an API across a myriad of factors—such as security, reliability, and functionality.

The testing can be performed with a testing tool, or via your own code, and the testing can be done at the message layer without a GUI (graphical user interface). The test itself essentially involves sending a request, obtaining the output, and recording the system’s response.

While GUI tests concentrate on the overall aesthetic of an application, API testing concentrates on the logic layer of software architecture. While it may be tempting to focus on the GUI for an excellent user experience, API is just as important, as it ensures that you catch bugs in the code.

The benefits of API testing

The benefits of API testing cannot be understated. You may have beta testing of an application, but not see a bug until it has already done damage to your organization. This is particularly important in terms of security.

Without testing, you will never know certain vulnerabilities in your application. Putting time into testing will exponentially improve software development and maintenance. Consider the following benefits to continuous testing of APIs.

Gives access to an application without the GUI

API testing allows Quality Assurance (QA) professionals to access an application without having to interact with a potentially disparate system. It helps you detect and recognize errors early and more quickly.

Testers can get data on your API even before the GUI is fully functional. This can expedite the time it takes your organization to launch new software or applications. For example, if you are developing software to work with a call controller action, you will be more confident early on that your program works.

Tests for core functionality

A program is worth very little if it does not work. API testing allows you to test the code-level functionality of an application early in the process. Even small errors can fester and become larger problems once you hit the GUI testing phase.

You can even automate this with QA automated testing. The automation of API testing allows your team to focus on development, while still keeping them updated on any potential problems. It will flag any security, multi-threading, reliability, or performance issues and let you know if the response data is not structured correctly (JSON or XML).

API tests also require extraordinary conditions and inputs. This means that it will protect the application from malicious code and breakage. It will test its functionality to its absolute limit which will help detect and ultimately remove vulnerabilities.

The types of API testing

While API testing is the general term for determining the quality of your application, there are many different types to consider during software development. It is a good idea to look at specific tests to ensure you are collecting all necessary data. Here are the different types of API tests:

Functional testing

This includes testing particular functions in the codebase. It runs through specific scenarios to ensure that API functions are handled well. The function of the API is tested with proper inputs and we should expect a few stated responses.

Security testing

Security should be a priority in any application or software you develop. You should always be testing for any vulnerabilities in security. This test ensures that your API is secure from external threats and includes the validation of encryption methodologies. It also tests the design of the API access control.

Here’s an example: You are creating an API for an electronic data interchange (EDI). The EDI helps send documents to clients and includes sensitive information. During security testing, you discover something is wrong with the encryption methodology. Your team averted a costly mistake and ensured your clients’ trust by catching the vulnerability before you went to market.

Validation Testing

A validation test occurs before an application is released. It verifies the aspects of the product, behavior, and its efficiency. It ensures that the application was developed successfully and is ready to be available to regular users.

Other tests

While we can’t go through each available test in detail, here are some overviews of other API tests you can perform.

Reliability testing: The API consistently connects and leads to reliable results.
Load testing: The API can handle a large number of calls.
Creativity testing: The API can handle being utilized in different ways.
Proficiency testing: The API increases the range of what developers can do.
Negative testing: Checks for every kind of wrong input the user can supply.

API testing best practices

Whether you are striving for software integration or developing an application, there are a few things you should do to ensure successful API testing. Here are some things to keep in mind when you begin your API tests.

Understand API requirements

Make sure you know the purpose of the API and the workflow of the application. Where is the API in the workflow? You need to understand the basics to make your intentions clear. The next person to use the test needs to know why you wrote it.

Specify the API output status

You need to verify the response status code in API testing. All API response status codes are separated into five classes. The first digit of the code defines the class of the response. Use these codes to determine the output of your API. Determine if the code follows global standard classes or if the code is specified in the requirement.

Focus on small, functional APIs

Don’t ignore the simple APIs that have only one or two inputs. These are necessary access points to further APIs. Focus on these before moving on to test the others to ensure that these initial points of access work. Robotic process automation can test these small APIs so you can focus on more complicated processes.

Additional tips

Leverage automation capability and automate wherever you can
Create positive and negative tests
Group cases by test category
Each test should be self-contained
Add stress to the system through a series of load tests
Use free Google Calendars to schedule regular tests and communicate a schedule with your team
Take special care with one-time call functions (Delete, CloseWindow, etc.)
Test for failure. You need to understand how your API will fail.
Prioritize so it will be quick and easy to perform your tests
Throw as much as you can at your APIs to test their limits
Finally, trust your instincts!

Final thoughts

APIs are an essential part of any application. They work in the background to make sure programs can talk to each other. Like call center queuing talks to your VoIP, it allows you to do more with the tech that keeps your businesses running.

While APIs run in the background, you can’t forget about them and focus on the GUI or the part of the software the user sees. While they can’t see it, users will definitely notice if it’s not working. With this in mind, go forth and make sure your APIs are working for you.

Elea is the SEO Content Optimization manager for RingCentral, the leader in global enterprise communication and collaboration solutions on the cloud. She has more than a decade’s worth of experience in on-page optimization, editorial production, and digital publishing. She spends her free time learning new things.