API’s are increasingly becoming the epicenter of today’s application development. As the primary mode of communication between web components, they are used to connect and transfer data and business logic across systems.

This means that thorough API tests can improve the quality of software and minimize significant security risks before production.

But before diving into more details about automated API tests, here’s a refresher on API testing.

What is API Testing?

API testing is the type of software testing performed directly at the API to verify whether it meets the expected functionality, security, reliability, and performance requirements. It usually tests the API without loading or interacting with the user interface, but by initiating direct requests to the API backend.

As illustrated below, API testing is done at the business layer- where all logical operations and transactions between the GUI and database layer occur. It is critical for software quality as it validates the logic in a build within a short time.

Unlike GUI testing, API testing can cope with shorter release cycles and regular changes

What types of API’s can you test?

APIs have evolved over the years- from simple code libraries that allowed applications to run code on the same device, to remote APIs that allow applications running on one device to call code hosted on another.

When choosing an API testing automation tool, it is important to understand the API technology you’re using and how to test it in the best way. The most common web service APIs include

SOAP (Simple Object Access Protocol)

REST (Representational State Transfer)

XML-RPC (Extensible markup language — Remote Procedure Calls)

JSON-RPC (JavaScript Object Notation- Remote Procedure Calls)

The Need for Automated API Tests

API testing can improve the efficiency of the entire test suite. At a high level, API tests help developers to validate solutions, maintain solutions, and eradicate errors.

However, if not performed thoroughly, problems can arise long after they were created. This could force development teams to halt the current sprint cycle and circle back to find what went wrong.

Discovering bugs later in the test cycle can impede development processes, which proves costly in the long run. By setting up automated API tests, you can:

Ensure that all services are running as desired

Confirm whether all endpoints are secure from unauthorized as well as unauthenticated users

Improve coverage for both functional and non-functional tests

Allow timely feedback to development teams and eventually quicker product releases

Test all application endpoints regardless of where they’re hosted, from AWS Lambda to your local device.

API tests allow you to validate the four main operations in web service APIs, i.e. the GET, POST, PUT, and DELETE methods.

Below is an example snippet verifying a JSON response received from a server using java rest-assured library

Assuming the response was something like this:

We can use REST assured to validate the response. A simple test in this case would be:

From the above code snippet, the function validateDataOnResponse() calls the API endpoint /data?id=254 and we receive a response in JSON format.

The test also verifies the statusCode as 200 and asserts that the response contains the name as “Tom” within its body

What types of API tests can you automate?

There are different types of tests that you can perform on an API. While the scope of testing differs from one API to another, most tests fit into one of these categories:

Functional testing — It focuses on testing specific functions within the application codebase. The aim is to ensure API functions are within the expected parameters, and if not, errors are handled appropriately. Ideally, this would include test cases verifying HTTP response codes, error codes, and responses.

Load testing — This type of testing is done to test how much load a specific unit or the entire codebase can support. It is especially necessary for applications that are designed to deal with huge data or multiple users.

To ensure peak performance, you need to identify whether the API can practically support the expected load, whether 500 requests, 5K requests, 50k requests or even 100k requests.

To ensure peak performance, you need to identify whether the API can practically support the expected load, whether 500 requests, 5K requests, 50k requests or even 100k requests. Security testing — Security testing is critical as it helps ensure your API implementation is secure against vulnerabilities. For this reason, developers should ensure their API test cases include checks to validate authorization, encryption mechanism, access control, session management, etc.

The API security verification and auditing process also involves fuzz testing and penetration testing, both that ensure your API is secure from external vulnerabilities

The API security verification and auditing process also involves fuzz testing and penetration testing, both that ensure your API is secure from external vulnerabilities Validation testing — One of the final yet highly crucial tests in API implementation.

It verifies essential aspects of product development, API behaviour, and overall efficiency.

This type of testing serves to validate whether API development and implementation adheres to the agreed standards as well as user needs and requirements.

It verifies essential aspects of product development, API behaviour, and overall efficiency. This type of testing serves to validate whether API development and implementation adheres to the agreed standards as well as user needs and requirements. Runtime/error detection — Unlike the above tests, which majorly focus on the results of implementing the API in a particular scenario, this type of test is concerned with how the API runs.

This includes monitoring for anomalies in code implementation, execution, error detection, and resource leaks.

Testing Strategy for APIs

One of the best practices when automating tests, not only for APIs, is configuring your test suite to provide an output such that you do not have to observe the system’s response.

Automated API tests can return any of these three outputs depending on the input conditions:

A boolean status- either a pass or a fail

Any type of data or information

A call to another API function or event

It is somewhat challenging to specify specific pass or fail scenarios when testing APIs directly.

There are scenarios when there could be no output or something unpredictable occurs. However, by comparing response data after a test or the behaviour after another API is called, testers can create definitive validation scenarios for their tests.

Performing comprehensive and rigorous API tests is a sure way of verifying your application works well from end to end.

However, to ensure code changes do not break your API and guarantee success in production, consider integrating automated API testing into your CI/CD pipeline.

Automate Your API Tests with Loadmill

One of the best testing practices is automating iterative test cases that can be re-used.

API tests are no exception- you need to run particular test cases repeatedly before every release. This means creating and maintaining from release to release can only be made easier through automation.

Loadmill supports API testing by allowing testers to record real user sessions in an application and converting the sessions into reliable test suites.

The process of creating recordings is super easy and only takes a couple of minutes. This eliminates the tiring and time-consuming process of scripting tests manually. You can also use the node module and CLI to run both API and load tests.

Test Automation helps development teams move faster and focus more on things that matter. With the increasing number of automation tools in the market, API testing is now easier than ever.