In the «Client-Server» architecture several computer clients (remote system) send requests and get services from the central service machine or server. More information about client-server architecture you can find in our blog article.
Web browsers interact with web servers with a help of HTTP (HyperText Transfer Protocol). When the link is clicked on the page, the form is filled in or the search is performed, the browser sends the HTTP-request to the server.
HTTP (Hypertext Transfer Protocol) is a protocol that allows the client and the server to communicate through the network by request/response. This protocol is similar to the application that relies on TCP/IP for its services. HTTPS – is the HTTP extension. It is used for secure communication over a computer network. The HTTP protocol is also used for transmitting requests and responses during the work with API.
API (Application Programming Interface) provides interaction between two systems. API allows sending information directly from one program to another, avoiding the user interface. This is an autonomous function which does not depend on other services. After clicking the interface button, the internal functions are launched to transmit and receive information. API accepts requests, transmits the information to the system, processes it and returns the response.
For the programs' interaction, their API should be built according to the same standard. One of them is REST (REpresentational State Transfer) which is a standard for the architecture of interaction between the applications and websites that uses HTTP. The peculiarity of REST is that the server does not remember the user's state between requests. In other words, user identification and all the parameters of the operation are transmitted in every request.
In general, REST covers a wider area than HTTP – it can be used in other networks with other protocols. REST describes the principles of interaction between client and server based on such concepts as «resource» and «verbs» (you can see them as subject and predicate). In the case of HTTP, the resource is defined by its URI and the verb is an HTTP method.
In the REST architecture, clients send requests to receive or modify resources, and servers send responses to these requests. Let us see the standard ways of making requests and sending responses.
REST requires that the client make a request to the server to get or change the data on the server. These requests usually include:
There are 4 main HTTP verbs used in requests for interaction with resources in the REST system:
In the request header, a client sends the content type they can get from the server. It is called ACCEPT field, and it guarantees that the server will not send data the client cannot understand or process. The options for the content can be MIME types (multipurpose extensions of Internet mail).
The MIME types used for determining the content type in the ACCEPT field consist of type and subtype. They are separated by a slash (/).
For example, a text file that contains HTML will be displayed with the text/html type. If this file had CSS it would be specified as text/css. The plain text file will be shown as text/plain. This default value is not the only one. If the client expects text/css and receives text/plain, it will not be able to recognise the content.
Other types and often used subtypes:
Thus, the client accessing the resource with id 23 in the articles resource on the server can send the GET request, for instance:
In this case the Accept header field indicates that the client will accept the content in text/html or application/xhtml.
Requests must have a path to the resource on which the operation should be performed. In API REST paths should be designed to help the client track events.
The first part of the path should be the plural form of the resource. This makes nested paths easy to read and understand.
Such a path as kidsfashion.com/customers/145/orders/17 is clear for every user because it is hierarchical and descriptive. The example shows that the order with ID 17 is accessed for the customer with ID 145.
Referring to a list or collection of resources is not always necessary to add an identifier. For example, the POST request to the kidsfashion.com/customers path does not require the additional identifier because the server generates an identifier for the new object.
If we try to access one resource, we need to add the identifier to the path. For instance:
GET kidsfashion.com/customers/:id – the element in the client resource with the specified identifier is received.
DELETE kidsfashion.com/customers/:id – the element in the client resource with the specified identifier is deleted.
API should also be tested. During its testing, we check the application programming interfaces. The purpose of testing API is to check functionality, reliability, performance and security of programming interfaces. In API testing instead of using the standard requests/conclusions (using the keyboard and others), we use the software for API requests, receiving and recording the response of the system. API tests are different from GUI tests and do not focus on the program's appearance. In general, such testing focuses on the business-logic level in the software architecture.
API testing refers to integrational testing, which means that during it there is a possibility to track errors in the interaction between system modules or between the systems. For this testing, special tools are used where you can send input data in a request and check the accuracy of output data.
Postman is an HTTP client for API testing. By using Postman you can:
Postman uses HTTP protocol to work with servers. The tester sends test requests from the client to the server and receives the answer to whether there is an error in API work.
Postman is available as an application for ОС Windows, macOS and Linux, as well as in the web version: https://www.postman.com/.
In the article, we will consider GET, and PUT requests and the responses to them. To create a request, you need to click the New button and choose the HTTP Request option.
It is necessary to create a collection where the Postman requests will be stored. Inside the collection, the requests can be grouped into folders, for example, by the different API versions or tested elements of the program.
Create the request by clicking the «Add requests» button.
Let's make a request to obtain data about the created user, for this select GET.
Enter the url of the site to be tested https://reqres.in/ (see more examples of requests and responses). API is closed on the majority of real websites for security reasons, therefore it is impossible to test it for a third-party user.
Write the name of the corresponding API, in our case it is /api/users/2.
Select raw in the «Body» tab.
Next, select the JSON text format (JavaScript Object Notation – a text format for data exchange in JavaScript).
The actual data about the user is displayed, which must be compared with the expected data.
Let's try to update user data by creating update_user. Select the PUT request.
Specify the data and send them.
As the result, you can see the specified update time and the 200 (successful) response from the server.
API testing is becoming more and more popular. Using it, you can predict how the system will react to a real user, perform the same tests with various sets of input data and take any additional actions by creating scenarios and test data, making the testing process faster and of higher quality.
