The attempts to understand the nuances of API testing services have a serious potential to give unprepared readers headaches. In this article, we’ll try to explain everything you need to know about API testing in the simplest way possible.
Let’s take a step back and start with the basics that allow QA specialists to work with APIs – client-server architecture and data transfer protocols.
A client-server architecture is a distributed application structure that partitions workloads between a service provider and its requester – a server and a client accordingly. It makes the application more secure, helps prevent access issues, and enables more users to run a program simultaneously.
Internet users have devices with different specifications and, thus, performance. Thanks to the client-server architecture, providers can guarantee equal (or at least close to equal) experience for all. Meanwhile, request processing, calculations, etc. are done on the provider’s end. Such an approach limits access to the source code and makes it much more difficult for a user to alter, making the system more secure.
There are three participants in this structure: client (user), server (hardware), and database (resources).
Servers work in tandem with databases. Everything that happens in a system is recorded in a database. For example:
All information on the web goes through the data transfer protocol known as HTTP (short for Hypertext Transfer Protocol). It is the foundation of every website. A computer uses HTTP to download a page from another computer somewhere on the Internet and show it to a user that requests the mentioned page at the moment. HTTP requests the necessary data (files, web pages, etc.) from a virtually remote system to display it on a local device.
Every HTTP message consists of three parts transmitted in the following order:
There are five groups of HTML status codes:
If an error is not matched and you don’t get a corresponding code displayed on the screen, you can use Chrome DevTools to get this information. Here, in addition to the status codes, you can find request methods, headers, and the rest of the request-related data.
Long story short, Chrome DevTools provides more information regarding requests and responses than you can access through the user interface. Besides, you can work with an API before the UI is developed. It allows catching numerous bugs in the early stages of software development and system design.
An API stands for an application programming interface. It is an end-point created by a developer or a company that allows using any features of a program in a different place or another program.
In a way, it is a contract, an agreement between two parties that regulates the way they share and process data. A client agrees and undertakes they will address a server in a specific way. The server assures to return the data or process them in a way specified by the client.
For example, create a user, save it to a database, and return an identifier signaling about success or failure. That’s an internal API.
Using third-party APIs is also a common practice. For example, if you want to add a weather forecast on your website, you don’t need to develop an app for that. It would be enough to “attach” an app that already exists – if it allows doing so. An API will connect you to the weather functionality, becoming an intermediary between your website and the weather app.
Anyone who interacts with a software system that uses an API can call it – directly or indirectly.
Direct usage of an API:
Indirect usage of an API:
Rumor has it that 90% of APIs in open access are REST APIs. REST is an architectural style for web services design. It was created to guide the development of the World Wide Web architecture. REST API is a set of functions and constraints defining how the architecture of the hypermedia systems should behave. In simple terms, REST defines the functions to which developers (or other systems) send requests and from which receive responses.
The interaction and data management process is entirely based on the HTTP protocol. Thanks to this, you can use REST API in probably any programming language. There is one downside, however: there is no hard-and-fast policy for REST API development. All resources on API are recommendations, not guidelines.
Just like any other type of testing, API checks allow us to find critical bugs before the system goes live. Apart from that, there are several specific particularities of API testing:
In general, you can cover APIs with the following types of testing:
There are some tips that will help you make API testing easier and more efficient. Some of them are quite universal, so you can apply them in other types of manual and automated testing.
Last but not least, keep your tests in order. Group them based on the categories where these tests belong. For example, if we are working with the functionality of user creation, all the tests should be related to this functionality. Don’t add order placement checks or something else to this scope.
Now, it’s time for a short overview of common mistakes and difficulties that pop up during the testing process. Here’s our top-5 rating.
There are a variety of combinations and parameters to use for testing a particular end-point.Choosing the right test design techniques is a solution.
The absence of a graphical interface can cause difficulties. Though it can be an advantage, it may also be complicated to test functionality without an interface, especially if you are new to API testing.
Data validation and verification can proceed differently in different systems. A server receiving data may not be able to read and process it due to the used type of data.
It is obligatory to check the processing of exceptions. QA specialists often forget about this one. To work with the exceptions you should know the rules of processing such data and requests. For example, try sending ‘null’ in a field supposed to feature data or sending a numeral instead of a string value.
Software testers need to have partial knowledge of programming. This one is controversial. If you know the basic understanding of client-server architecture, it is enough for API testing. On the other hand, even programming knowledge will boost your skills.
There are a variety of tools for working with API. Some of the most widely used are:
As the experience shows, the greatest share of automation tasks falls on Postman API testing. Nevertheless, getting familiar with a variety of platforms is always a benefit for a QA specialist.
API testing can seem pretty difficult, but with the right resources at your disposal, you’ll figure out the secrets quickly. Good luck with your studying and practice 😉
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