Testing API Methods A Comprehensive Guide

Testing API Methods: A Comprehensive Guide

Ever wondered how computers interact with each other, what happens behind the visible screen when systems process the user request. The answer is simple and interesting, we humans use verbal and non verbal communication to communicate with one another, similarly the computers use  Application Programming Interface to interact with one or more computers that are connected over the internet without user intervention. The API testing methods help validate the API set-up of the application.

What is an API?

Application Programming Interface commonly called as API, is an integral part of software testing. It deals with testing the application interface from the backend layer based on the application’s logic. It follows a request and response protocol for communication, the  request is from the client and response is from the server side. Here the client is usually the front end software and the server is the backend logic. 

The application interface holds the information of the internal details of how the system functions. These are not directly accessed or visible to the end users, the programmers can build tailored API for the specific system or a shared one that allows others systems to access supporting interoperability.  Which is why the design of the API highly depends on the software architecture. 

At a high level we can say that both systems and softwares use APIs for accessing and executing purposes. The API specifications either showcase its behavior or the way in which it links with other APIs. It helps in standardizing the data flow and data exchange between web services. When the specifications are met and are used, making it available for customer interface then that is implementing or exposing the API.   

How API Works

There are different types of APIs : 

  • Private APIs : It is built and assessed specifically for a particular organization and only used in-house. 
  • Partner APIs : The company provides access to potential customers or partners based on agreement 
  • Public APIs: The access is open to public developers and used for commercial purposes. 

What are API Methods?

When we speak of API methods, the Web APIs use HTTP protocol for communication. As we know it follows the client server model, where the client sends the request and the server responds. There are many ways in which HTTP sends requests,which are the HTTP verbs and referred to by the value of their request method property.  The important and most commonly used API methods  are: 

GET request 

  • This is most common request and it is used to request data from the server 
  • It retrieves and represents the exact data present and does not modify or perform task
  • Even if multiple identical requests are made, it returns the same result, this is called Idempotent 
  • The Get request follows the read method from the CRUD operations  


  • Get API used to load a website or navigate to a landing page 
  • To get the popular items in a particular category, say latest filter applied  for new products under home decor section on a ecommerce website 

POST  request 

  • It is used to send the data to the server to create or update a resource, therefore data mutation happens. 
  • When same request is sent twice, it leads to duplication, it is called  Non-Idempotent
  • The Post request follows the create method from the CRUD operations 


  • When creating a new user account in gmail, it sends a Post request. 
  • While registering for a webinar on a site, the Post API is used. All the data entered in the field are put in the response body of the request and sent to the server 

PUT request 

  • It is used to send data to the API for creating or updating an existing resource.
  • The difference between Put and Post is that the Put API is Idempotent.
  • Put will replace the resource in its entirety 


  • Editing an existing students record in the student’s portal 

DELETE request 

  • It is used to delete a single or list of resources, more commonly found in RESTful API. It has to be used with caution. 
  • Multiple identical requests for deleting the same resource will return a 404. 


  • Delete API is used to remove the irrelevant user data from the records 

What is API Testing? 

Software testing is done to check the quality of the software. Since API is the code that enables connection and communication between two software programs, the presentation layer and the backend database. It is important to check whether or not the APIs are connected properly.

API testing is one of the software testing practices where we test the APIs directly for its functionality, on its reliability, the performance, and most importantly the security. APIs are also tested as a part of integration testing, since the design of the software architecture and design of API are highly interdependent.

An overview of the process flow to conduct API testing is as follows: 

Step 1: Understand and review API specification 

Step 2: List down the API testing requirements 

Step 3: Build the API testing strategy and API testing methods 

Step 4: Set up the API testing environment 

Step 5: Run tests using both positive and negative scenarios 

Today most companies follow the concept of shift left testing, testing from the early stage to avoid bottlenecks. So testing starts from the bottom of the pyramid and goes all the way to the top. The bottom layer is the unit layer, where the developers perform code tests by writing unit test cases. Moving to the second level which is the server level where the API testing is done. It is then followed by the UI testing using GUI tests.

API Layer

Why test API methods? 

With a huge number of API requests churned out each day, API testing is needed because it helps in validating if the API setup performs as expected and returns output as intended. The tests will cover API functionality, reliability, performance and security. 

The reason why API testing is important is because of the following reasons: 

  • API testing process is done before UI testing and it helps identify and eliminate most of the server level errors. Also, API testing consumes less testing time and testing cost than GUI testing
  • Since the API testing process helps in code-level functionality validation, it helps in identifying the small bugs before it turns into a critical one. 
  • It helps in securing and optimizing the communication between servers and systems. It also focuses on checking if the business logic laid down is correct at the API level. Since it also includes dealing with sensitive data, checking for API security is crucial. It checks the APIs for compliance and security. 
  • By ensuring the APIs perform as expected it helps to safeguard the business reputation for quality assurance in the minds of the customer and help them develop trust. 
  • Checking and aligning the API testing strategy with CI/CD pipeline is important as  it provides room for faster release cycle with reduced number of errors. 

What is meant by Testing API Methods? 

Once the API set up is ready, it is tested based on the  API testing methods. There are several ways to test the APIs and that can be done both manually and automated. From developer to testers to the DevOps engineers all create API testing strategy to conduct crucial tests in order to check and validate the API setup and its integration from end to end. Testing individual services or endpoint can be easy, but what is more important is to test the framework completely and eliminate errors in the setup at the earliest

How to test different API methods 

Manual ways to test APIs 

In Manual testing, the testing is done manually without the use of test scripts.

Exploratory testing: Just like the name suggests the testers explore the application to identify bugs. Testers could do black box testing by sending the requests to API and check if the desired output is received. In case of white box API testing, the testers usually try to find out and validate the API functions using the source code. 

Usability testing: This type of testing depends on the API structure, usability goal and user segment. The API structure has to be reliable and usable. This testing is majorly user-centric, and the testing is carried out mimicking how the target user group  would use the software. It helps validate the product’s functionality from the end users perspective. 

Ad.hoc testing: It is usually carried out after the formal testing is done. The testers randomly test the product to check for any loopholes. It is done to check the stability of the overall APIs integration. It is mostly done when minor tweaks or new features are added to the product, the testers will right away check the specific update without any pre-defined planning or documentation of test cases. 

Automated ways to test APIs 

In automation testing the tests are automated using automation frameworks or tools. 

Functional testing: It is performed to validate if the API performs as expected. The functionality of the API is tested using both positive and negative test scenarios to see if it returns the intended output. The API has to be well built to identify the valid and invalid requests  Functional API testing can be a little challenging because of the lack of GUI. So the functional testing testing of API starts with verification of authentication process 

Load testing: This is mainly to see how the API functions under heavy traffic. Based on the requirements, it involves stimulating a large amount of request volume and checking the response output and response time (ranging from per second or per minute to per hour)  and looking out for errors. It is to check how the API operates under load. Load testing is carried out in regular intervals to record the performance benchmarks and breaking point of the APIs. 

Security testing: The APIs along with its basic functionality also have security requirements listed down, such as authentication and access control. It is to protect the data and application from hacker attacks. 

Regression testing: Testers prefer regression testing when their application is updated at frequent intervals, for example if new features are added during every sprint, and when there is a need for repeated testing. It helps to save time and efforts in re-running the test scenarios multiple times.

Searching and selecting the right tool for API testing and forming an API testing strategy is a crucial step. Testsigma is a low-code test automation platform, where tests are created using NLPs . Since it is low-code it does not require any prior coding knowledge and also helps non-coders to perform testing with ease. 

Testsigma also provides Integrated Automated API testing. Testsigma’s API testing capabilities helps automate API testing for web, mobile and desktop applications using Natural Language Programming. It  becomes a one stop solution for test management, test authoring, test execution and reporting without expertise in coding languages. 

It enables the creation of tests for REST API methods – GET, POST, PUT, DELETE, PATCH, thereby providing complete all inclusive test coverage for APIs. It also supports data driven API tests and validates expected vs actual responses in real time and reflects the errors in the test status and test reports. 

Challenges in testing different API methods 

Aligning the Initial setup of APIs with the requirements and sequencing the API calls is a mandatory step and it takes time and effort. In order to reduce manual intervention in API testing, identifying, automating and validating the tests can be initially challenging. 

  • Checking the system integration for APIs  is a major task performed focusing more on the API design to evaluate its performance and validate each and every response to check if all the API calls are working properly. 
  • Every time there are changes such as a new feature update or enhancements, it is necessary to keep track of the API tests and the impact on the API test automation process setup.
  • Validating the API parameters correctly and setting up required checkpoints is an important step to avoid security or stability issues. 
  • Updating schema of API tests is a significant step, since schema provides the API syntax and grammar of the test documents, it is important to update the schema accordingly on every update and maintain it through the testing process. 
  • It is a critical decision making process on choosing the right tool for testing API that fits the budget and also meets the API testing requirements. 


In today’s modern business environment, API testing is blooming and is an essential part of developing the application. Conducting the automated API testing not only helps in time and cost saving, it also makes it an integral part of the CI/CD pipeline. It enables the business to provide quality applications and better user experience to the customers.

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