It is common knowledge that testing is vital in any development process, ensuring a bug-free and highly functional final product. This is also the case when we perform API testing. 

Application Programming Interfaces (APIs) can be described as the doorway into any app or website, where third-party apps can access all data and features built without needing custom code. Generally, developers use APIs to interact with products and programs that have different code and features than theirs, without the need to implement said code into their own products.

APIs allow for early-stage testing of security, functionality and reliability before the UI(user interface) is developed.

API testing usually consists of sending API requests in HTTP or REST formats and getting a reply from the app or server in JSON or XML formats.

Let’s explore the meaning of the REST format, definitions of REST APIs and 5 of the best practices in performing REST API testing.

What is REST? What are REST APIs?

REST (Representational State Transfer) is a long-established API framework that rose to become the latest standard for APIs. The REST format is widely known and used by over 80% of public web APIs (RESTful apps). Its primary function is to bridge the communication gap between clients (e.g. web browser apps) and servers while conforming to distinct build constraints.

The API requests are usually sent in HTTP format, and these main functions are:

• POST (creates the resource)

• GET (fetches the resource)

• PUT (updates the resource - replaces the info)

• PATCH (updates the resource - modifies the info)

• DELETE (deletes the resource)

For a robust testing process down the line, REST APIs must be designed appropriately. The key points to consider when doing this are security, using a complete API testing tool, and ease of use for API consumers/providers.

5 Best Practices for REST API Testing

1. Use an all-inclusive API testing tool.

A thorough API test process requires a complete and up-to-date testing tool. Investing in an all-inclusive, powerful testing tool allows for an easy testing process that accurately helps you keep track of functionality and performance. 

2. Perform sanity and smoke tests first.

It’s an excellent practice to start the REST API testing process by performing some shallow, probing, positive functional tests. This is often referred to as Smoke Testing or Sanity testing. These help testers check key functionality or verify whether the actual API responds to API calls as expected. 

When undertaken as early as possible, smoke or sanity testing ensures that the key functions of the product are within normal working parameters and working as predicted, thereby ensuring the program's stability.

3. Well-written documentation.

A very overlooked aspect of good REST API testing has to be well-compiled API documentation. We can think of it as our virtual business card, the first thing that falls in the hands of our customers trying to understand the product. Easy-to-use documentation can be the deciding factor in our business transactions; therefore, it is recommended that we have one of good quality.

Developers interested in using your product have to understand your API first. The more precise and thorough the documentation, the faster they will start using your program.

Giving your customers an easy walkthrough of your API system is simple and must include relevant information such as compatible methods, endpoints or parameter options.

4. Test Positive and Negative Outcomes.

The main focus of REST API testing is positive outcomes(the data we input is correct, and requests go through accordingly), but sometimes we should perform tests on the opposing side too. In doing so, Devs can check that the API supports receiving invalid data without crashing or stopping. Graceful handling of invalid data should take the form of error messages or other indications of a problem that can be handled without the need to pause the testing process.

5.  Keep security in check.

Since we mentioned APIs are doorways into our app or program, we shouldn't allow just anyone access to them.

Through the use of APIs, private and critical data is exchanged between the client and server that can become a target for cybercriminals. A successful attack can impact end users and damage your application and your company’s reputation.

It is good cybersecurity hygiene to have an SSL or TLS security protocol that offers an encryption link between the client and server.

REST APIs should only communicate over secure channels, as there is no need for the information to be out in the open. Users should receive only the information they request and no more, which is a risk if the API is made available through unsecured channels.

Regular security tests should be fundamental to ensure that all protection layers function as intended.