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Beginners Guide to API Testing 1

Beginners Guide to API Testing

Introduction to API

APIs, or application programming interfaces, have grown to be an essential aspect of software development and technology in general. They enable data interchange and communication between many applications and systems. In the current digital era, APIs are utilised in all aspects of life, including social media, banking, healthcare, mobile apps, and cloud services. It is essential to make sure that APIs are operating properly and satisfying user needs given the exponential growth in the number of APIs.

In this blog, we will explore the basics of API testing, its importance, different types of APIs, and what to validate in API testing. Whether you’re a developer, tester, or QA professional, this blog will provide you a thorough introduction to API testing, along with advice on how to get started and best practices.

What is API Testing?

API testing is a process used to assess the performance, security, and usability of APIs. It aids in finding bugs, problems, and security weaknesses and makes sure the API generates the desired results.
Testing an API’s functionality and if it meets stakeholder expectations are the two main goals of this process. The test needs to cover a wide range of topics, including input validation, managing errors, security, performance, and reliability.

Why do we need API testing?

Due to its role in ensuring the application’s dependability and quality, API testing is a crucial phase in the software development lifecycle. The need for API testing is dictated by a number of factors:
Functional Validation: API testing ensures that the API is operationally sound and complies with all criteria. Testing for appropriate input and output, error handling, and general behaviour are all included in this.

Ensure compatibility: API testing ensures that the API is compliant with the various systems and programmes that it may need to integrate with. This includes testing for compatibility with various platforms, operating systems, and programming languages.

Performance Improvement: API testing is a useful tool for locating performance bottlenecks and problems, such as sluggish response times and high resource usage. The performance of the API can then be enhanced using this information.

Identify Security Vulnerabilities: API testing aids in the discovery of security flaws, such as those in authentication, encryption, and authorization. This aids in preventing security lapses and safeguarding sensitive data.
Overall, API testing is essential for assuring the application’s quality, dependability, and security. Early problem detection and resolution enhances the user experience by lowering the likelihood of production-related issues.

Types of API

There are majorly three types of API REST, SOAP & GraphQL.

REST (Representational State Transfer)

It is a software architectural style for building web services. It defines a set of constraints to be used for creating web services.
REST uses HTTP methods (such as GET, POST, PUT, DELETE) to interact with resources, where a resource is a data object (such as an article, a customer, or an order).

Example: A RESTful web service to retrieve a list of articles might use the following URL:

GET https://api.example. com/articles

SOAP (Simple Object Access Protocol)

It is a messaging protocol for exchanging structured data in the implementation of web services. It uses XML as its message format and can be carried over a variety of lower-level protocols, including HTTP and SMTP.

Example: A SOAP request to retrieve a list of articles might look like this:

<soap:Envelope xmlns:soap=”http : // www . w3 .org/2003/05/soap-envelope”>
<ns2:getArticles xmlns:ns2=”http : // www . example. com/articles”>


It is a query language for APIs that was developed by Facebook. It provides a more efficient and flexible alternative to REST and SOAP by allowing the client to request exactly the data it needs and nothing more.

Example: A GraphQL query to retrieve a list of articles and their titles might look like this:

query {
articles {

API Methods

The numerous operations or actions that can be carried out utilising an API are referred to as endpoints or API methods. They specify how an API can be applied to obtain data or carry out activities on that data.

Some of the most common API methods are GET, POST, PUT , PATCH & DELETE.
Let’s try to understand each one of the with example:


This method is used to retrieve data from a server. You can use it to retrieve one or more resources from an API; it is a read-only operation. A GET request only includes parameters that specify the resource to be retrieved; no other data is supplied to the server during a GET request.
For example, if you want to retrieve information about a specific user, you would send a GET request to the API with the user’s id as a parameter.


It is used to delete data from a server. It is used to delete a specific resource identified by a unique identifier, such as a user id. When making a DELETE request, you are sending a request to the server to remove a resource. DELETE is a destructive operation, and it is essential to be cautious when using it.


It is used to update a resource completely. It requires the client to send the complete resource representation. The PUT method is idempotent. So if you retry a request multiple times, that should be equivalent to single request modification.

Example: Updating a user’s profile information.


It is used to partially update a resource. It requires the client to send only the changes.
Example: Updating a user’s password.


It is used to create a new resource. It requires the client to send the representation of the resources to be created. POST is NOT idempotent. So if you retry the request N times, you will end up having N resources with N different URIs created on server

Example: Creating a new user account.

For RESTful APIs, PUT method should only be used if the client can update the entire resource, while PATCH can be used if the client can update only a part of the resource.
The POST method should be used to create a new resource.

Types of Validation in API Testing

There are usually three main types of validation in API testing:

1. Status code validation
2. Response body validation
3. Schema Validation

Status Code Validation

Status code validation in API refers to the process of verifying the HTTP status code returned in the response from an API. An HTTP status code is a message a website’s server sends to the browser to indicate whether or not that request can be fulfilled. Status code specs are set by the W3C. Status codes are embedded in the HTTP header of a page to tell the browser the result of its request.

For example, you could write a test case that makes a request to the API to retrieve the details of a specific book, and then verifies that the API returns a 200 OK status code. If the API returns a different status code, such as a 404 Not Found status code, the test case would fail and an error message would be returned indicating that the API is not returning the expected result.

Response Body Validation

When referring to an API, the term “response body validation” describes the procedure of examining the information contained in the response that the API has returned after receiving a request. The data or information the API client requested is contained in the response body, which is an essential component of the API response.
Response body validation can be carried either manually or automatically, and a number of tools are available to assist with automation. For instance, you can construct test cases that validate the response content and automatically determine whether it satisfies the required standards using Postman, SoapUI, or other API testing tools.

Schema Validation

Schema validation in API refers to the process of verifying the structure and format of the data returned by an API against a predefined schema. The schema is a blueprint or template that defines the structure and type of data that should be returned in the response.
For example, consider an API that returns information about books. The schema for this API might define the structure of the response as follows:
“type”: “object”,
“properties”: {
“book_id”: {
“type”: “string”
“title”: {
“type”: “string”
“author”: {
“type”: “string”
“year_published”: {
“type”: “integer”
“required”: [“book_id”, “title”, “author”, “year_published”]

In this example, the schema defines the structure of the response as an object with four properties: “book_id”, “title”, “author”, and “year_published”. The schema also specifies the type of each property (e.g., string, integer), and it requires that all four properties be present in the response.


By ensuring the API’s reliability and quality, API testing can improve the user experience while reducing the possibility of errors or failures.
Collaboration between development teams, testing teams, and other stakeholders can be enhanced via API testing, which will improve communication and speed up problem solving.
In summary, API testing helps to speed up the development process, cut expenses, and help businesses improve the quality, security, and dependability of their apps. Businesses can benefit from a high-quality, secure, and effective application development process by investing in API testing.

Sidharth Shukla

Sidharth Shukla

Currently working as a SDET. He is an Automation enabler who provides solutions that mitigates quality risk. Passionate about technical writing and contribution towards QA community.

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