A Detailed Guide To REST API Testing | Preflight's View

Application Programming Interface or API is a computing interface that is described as a bridge that enables two different systems to communicate and exchange information. In our previous articles, you must have read about how important APIs are and why it is so crucial to test them thoroughly for proper performance.

Now, here we will be focusing on REST API, a highly important API that plays an important role in the interaction with RESTful web services. It might be more useful for tech businesses that have huge teams of engineers because if such a large number of engineers create multiple endpoints for every single product, it becomes a cumbersome task to manage everything. Anyways, let’s move on with the article to understand it better.

You already know how API testing is performed with the objective of determining the functionality, performance, dependability, and security of the APIs. In those tests, API calls are made using software instead of normal user inputs, and responses are recorded to check the correctness of the API’s performance. Now, let’s see how those strategies work for REST APIs.


REST API or RESTful API is an API that follows the limitations of Representational State Transfer or REST, and helps in maintaining a fast, flexible, and simple interaction between RESTful web applications. REST APIs are the most used API format as over 80% of public APIs are RESTful.

Though stateful REST APIs are said to be compatible with any protocol or data format, they mostly communicate through JSON, HTTP, XLT, XML, HTML, or simple text. Out of these data formats, JSON is preferred due to its compatibility with most languages.

Due to their adaptability, REST APIs are highly useful for complex services. Also, with their ability to process commands from multiple users and different data formats, REST APIs are widely used in various industries such as IoT or e-commerce.

What Is REST API Testing?

REST API testing is a useful open-source automation technique that checks if the RESTful APIs are properly working for web apps. Though it is mostly used for testing JSON and XML-based web apps, it is compatible with all methods such as GET, POST, PUT, PATCH, and DELETE.

This test is performed by sending HTTP or HTTPS requests and recording the response of the REST API to check whether it is functioning properly or not. The above-mentioned methods i.e. GET, PUT, POST, PATCH, and DELETE are used in this form of testing.

Now, let’s check out some details about the four main types of API testing methods.

  • GET: This is the method where information is collected from the server through a URI or Uniform Resource Identifier. In this method, you must make sure that it only extracts information and does not affect data in any way.
  • POST: You can use this method to create new entities besides sending data to the server. You can perform data-sending operations such as uploading files, sending customer information, etc. through HTML forms.
  • PUT: This is the method where an entity is updated or a new one is created.
  • DELETE: This method can be used to remove existing representations of the target resource provided by a URI.

Different Ways of REST API Testing

Based on the paths, you can perform REST API tests in the following two ways -

  • Manual Testing
  • Automation Testing

Procedure of REST API Testing

As the objective of these tests is to ensure that the REST APIs are working properly, the main procedure of doing that involves an interaction between an application and a sample API. The two primary requirements of API testing are mentioned below.

  • A tool or framework that will operate the API.
  • Codes that will test the sample REST API. Make sure that the code is written by the tester for maximum efficacy.

Tools used for REST API test cases are -

  • Advanced REST Client
  • Postman-REST Client
  • Curl in LINUX

You will get to know about Advanced REST Client by the following portions in this article.

However, the good news for you is that Preflight lets you create and execute effective UI test cases that can eventually be extremely useful for testing different APIs used in your application. You can get every piece of information that you need from our website as well as our detailed documentation.

How To Get Advanced REST Client?

Follow the below-mentioned steps to get Advanced REST Client -

Now, as you have got Advanced REST Client, it’s time to test the RESTful API.

Steps To Test RESTful API

Here are the steps for the case of using the REST Client extension in Google Chrome. When the installation is done, proceed with the following steps for testing RESTful API -

  • Open Advanced REST Client. That means when it is installed, launch it.
  • In the textbox, enter the URL of the API you want to test.
  • Select the HTTP method in API testing (e.g. POST).
  • Give Headers set in the Headers textbox and click Insert headers set.
  • Click on “USE THIS SET”.
  • Provide the body content through the following method -
  • Open the Body Tab.
  • Select Body content type and Editor View.
  • Select the Editor view as “Raw input”.
  • Go to Payload and pass the request body of the API to test as in key-value pairs e.g. {“key-1”:”value-1”, “key-2”:”value-2”}. In the case of post API, pass body or parameters.
  • To start testing, submit the details by these steps -
  • Click “Send”.
  • Click “DETAILS” to view Response headers.

Check The Authenticity of The Results

The goal of performing any form of test is to compare its obtained results with the expected results. And, in the case of web API testing, it is primarily determined by the API’s response code, response message, and response body. We have jotted down different response codes and their meanings.

1xx Informational

4xx Client Error

100 Continue

410 Gone

101 Switching Protocols

411 Length Required

102 Processing

412 Precondition Failed

413 Request Entity Too Large

2xx Success

414 Request-URI Too Long

200 OK

415 Unsupported Media Type

201 Created

416 Requested Range Not Satisfiable

203 Non-Authoritative Information

426 Upgrade Required

204 No Content

428 Precondition Required

205 Reset Content

429 Too Many Requests

206 Partial Content

431 Request Header Fields Too Large

207 Multi-Status (WebDAV)

451 Unavailable For Legal Reasons

Already Reported (WebDAV)

499 Client Closed Request (Nginx)

226 IM Used

5xx Server Error 

3xx Redirection

500 Internal Server Error

300 Multiple Choices

501 Not Implemented

301 Moved Permanently

502 Bad Gateway

302 Found

503 Service Unavailable

303 See Other

504 Gateway Timeout

304 Not Modified

505 HTTP Version Not Supported

305 Use Proxy

506 Variant Also Negotiates (Experimental)

306 (Unused)

507 Insufficient Storage (WebDAV)

307 Temporary Redirect

508 Loop Detected (WebDAV)

308 Permanent Redirect

509 Bandwidth Limit Exceeded

510 Not Extended

4xx Client Error 

511 Network Authentication Required

400 Bad Request

598 Network Read Timeout Error

401 Unauthorized

599 Network Connect Timeout Error

402 Payment Required

403 Forbidden

404 Not Found

405 Method Not Allowed

406 Not Acceptable

407 Proxy Authentication Required

408 Request Timeout

409 Conflict

GraphQL vs REST

GraphQL is a renowned application layer server-side technology and REST is a popular API that can be compared with it on multiple grounds. Hence, the below-mentioned detailed comparison between them can acknowledge you a lot.



It is an application layer server-side technology that is used for executing queries with existing data.

It is a software architectural style that is considered as a conventional standard for designing APIs.

It can be organized in terms of a schema.

It can be arranged in terms of endpoints.

You can use a single endpoint to deploy it over HTTP. That endpoint provides the full capabilities of the exposed service.

It can be deployed over a set of URLs where each one of them exposes a single resource.

GraphQL follows client-driven architecture.

REST follows server-driven architecture.

It does not come with an in-built caching mechanism.

It caches automatically.

It has a fast development speed.

It has a slow development speed.

It does not require API versioning.

It supports multiple API versions.

You can separate the identity from how you fetch it.

The identity of an object is the endpoint that you call in REST.

The response output is in JSON.

The response output is commonly in XML, YAML, and JSON.

It provides high consistency across all platforms.

It is difficult to get consistency across all platforms.

It offers type-safety and auto-generated documentation.

It doesn’t offer type-safety or auto-generated documentation.

The server determines available resources.

The server determines the shape and size of the resource.

It allows schema stitching and remote data fetching.

It requires expensive custom middleware to simplify work with multiple endpoints.

It is strongly typed.

It is weakly typed.

GraphQL mutations must have a string message format.

REST mutations can have any message format.

For query validation, it uses metadata.

It does not have cacheable metadata that can be read by machines.

It has single endpoints.

It has multiple endpoints.

It has partners that require API customization.

It offers flexible public API that is capable of easily enabling new applications.

It can provide consistent and high-quality UX across all operating systems.

It can be difficult to get consistency across all operating systems.

Challenges In REST API Testing

The challenges that you may face in REST API testing are kind of similar to the ones that you may face in generic API testing. So, take a look at them carefully.

  • As the goal of API testing is to verify the proper working of APIs and detect failures, the tests often have to change the parameters of API calls. This practice gets you involved with exploring edge conditions and assigning common parameters.
  • To identify the content in which API calls are done, you need to set environment conditions, such as peripheral devices, files, etc. and have to internally store the data that influences the API.
  • It becomes a great challenge to make parameter value combinations for calls with multiple parameters.
  • Obtaining useful results from API from successive calls is a difficult task.
  • You have to order the API calls based on the sequence function that is to be executed.


From the article, you can clearly see that REST API testing is an extremely useful practice that helps you ensure that your REST APIs are working properly. Here we have jotted down a compact and useful portion of everything you need to know about this crucial form of API testing. Hence, you must consider going through this article carefully to acknowledge yourself with a lot of information.

While this article can significantly help you decide how you should proceed with your REST API tests, you must know that using advanced test automation tools like Preflight is the step you need to take first for achieving great test efficiency as well as test coverage. It is a supremely powerful yet simple tool that can let you solve all your test automation needs within seconds without demanding you to be skilled in coding. And, you can be a part of our amazing community by just signing up with us.

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