API Testing – Factors to Consider

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What you need to know about API Testing

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Last updated on June 21st, 2024

APIs or Application Programming Interfaces are embeddable software functionality that allows different cloud-based or server-side applications to communicate with specific software programs loaded on devices and endpoints or that allow different components of software programs to communicate with each other based on specified rule. These software programs exposed to the end user are usually in the form of web-based applications. 

As such, APIs are now considered to be technology tools for businesses across all industries. APIs offered by various cloud-based vendors allow businesses to IT enable their workflow quickly, resulting in expansion, growth, and profits. Adoption of innovation into the business also becomes easier as software and solutions do not have to be written from scratch; custom solutions can be built quickly using APIs as building blocks.

IT teams of various enterprises can use these APIs and embed these service offerings within their custom application relatively easily and within short periods. Using vendors that specialize in such development and integration is now considered common practice.

What Are the Types of API?

IT teams have a varied choice of APIs that can be used depending on the cloud-based services they wish to integrate into the software as well as the backend providers to be used. To that end, open APIs are public domain APIs that are usually free or based on subscription models. 

There are partner APIs whose use is restricted to only those enterprises that are in some kind of business relationship with the partner providing the APIs. At the same time, internal APIs are developed in-house solely for the use of that organization. 

What Are the Types of API Architectures?

APIs can communicate with their hosts and embedded environments with different protocols and architectures. The API is then used as per the rules, structures, and constraints of that particular architecture and protocol. 

The commonly used API protocols and architectures are REST, SOAP, and RPC. Choosing a protocol and architecture is based on factors such as operational complexity, performance, security, allotted development time, etc., and is usually done jointly by the in-house IT team and SaaS product development partners

What Is the Importance of API Testing?

As mentioned above, APIs are building blocks that an enterprise uses to create customized software based on the services of a cloud vendor or similar. These building blocks or software code have been written by the service vendor external to the enterprise, which might or might not follow the quality assurance standards and practices as that of the enterprise which has embedded these APIs into their custom software. 

API imported and embedded into any software should be tested for reliability and performance. The API should work as per compliances and conditions as prescribed with the testing protocols of the enterprise. Partnering with Quality Assurance experts to ensure adherence to these prescribed standards increases deployment productivity substantially. 

How Does API Testing Differ from Other Forms of Testing?

API testing is very different from other forms of testing, such as unit testing and functional testing. Unit and Functional testing focus on code, portion, or whole for a given functionality or purpose. APIs are embedded into software code for a specific predefined purpose. And only those APIs and their functionality must be tested within the framework or architecture of the software code they’re integrated into. 

This can be done in the early stages of the SDLC and across the cycle until deployment. API Testing service providers specialize in this differentiation, and strategic partnerships are formed to achieve the goal of timely quality code deployment.

How To Approach API Testing?

The testing of Web API and Web Service API should be planned, and the API documentation available should be carefully studied before proceeding. A testing checklist based on compliances and protocols as adopted for API testing in that enterprise has to be drawn up.

Once the usage of the API is understood, the API can be inserted into the code and testing can begin on devices or endpoints on which these APIs will be called. How the API behaves by way of its responses based on various inputs passed to it is to be carefully checked. These input parameters could be both erroneous, correct, or even garbage and the response of the API to that input has to be checked, logged, and compared with the testing checklist as prepared. 

An advantage available while testing API is that the software product does not have to be completely ready for API testing. A basic framework of the software code in which the API is to be embedded is sufficient for the preliminary testing of the API. This ensures that API testing can be done in the initial stages of the software development life cycle itself.

What Are the Common Types of API Testing?

To ensure complete quality assurance of a software product and the cloud services used via API, the product, both as a whole and on a unit level, must be tested thoroughly. Each unit and the application will have API embedded within it, and each scenario will have to be tested.

User Interface Testing

Ease of user interaction defines the level of customer experience. The cleaner, easier, and more accurate the user interaction, the better the customer experience. Testing is done to ensure that the user interface and the associated APIs accept and give responses as required with expected stability, speed, and consistent performance.

Load Testing

Load testing is crucial in measuring the performance of the APIs during peak usage. This testing checks for the amount of traffic and user requests that the application and API can accept, sustain, and process successfully at a given time. It is done both at the application level and the individual API level.

Exception Handing Testing

The integrated APIs and the application as a whole are both deliberately tested with various conditions of incorrect parameters and handling. The resultant behavior of the API is monitored as to how these errors and exceptions are handled and their effect on the overall performance of the application and user interaction experience.

Security Testing

Adherence to security compliances and protocols are crucial prerequisites to deploying any software. The APIs must be thoroughly tested for security vulnerabilities and possible compromises that could lead to any cybersecurity breach. The APIs must also be tested to ensure their security rating is within the required compliances and protocols defined for the enterprise.

API Testing Tools

Enterprises can choose to make their custom-built testing jigs for API testing or use already available technology tools. This, however, requires time and skills to build the appropriate framework and constant maintenance and upgradation are imperative.

An easier alternative is to use third-party API testing tools, which are easy to use, need minimal coding skills, and a moderate level of expertise to deploy the tests. Swagger, Postman, and Jmeter are some of the popular and most commonly used tools for API testing. API testing can also be automated, thus increasing productivity and freeing up resource allocations using tools such as Katalon.

Click here to learn more about our Quality Assurance and API testing services. And contact us for a free consultation.


What are the key factors to consider when planning API testing?

Key factors include functionality, reliability, performance, security, documentation, and data validation. Functionality ensures the API performs its intended functions. Reliability checks the API’s ability to consistently perform required functions under various conditions. Performance assesses the API’s responsiveness and load-handling capabilities. Security ensures the API is protected against threats and vulnerabilities. Documentation verifies that API documentation is clear, accurate, and comprehensive. Data validation ensures the API correctly processes input and output data.

How do you test the functionality of an API?

Functional testing of an API involves unit tests, integration tests, and validation tests. Unit tests check individual endpoints for expected results. Integration tests ensure the API works well with other systems and APIs. Validation tests check the correctness of responses, including status codes, headers, and payload.

What performance aspects should be tested in API testing?

Performance aspects include response time, throughput, scalability, and stress testing. Response time measures how quickly the API responds to requests. Throughput evaluates the number of transactions the API can handle within a specific period. Scalability determines how well the API handles increased loads. Stress testing examines the API under extreme conditions to see how it performs beyond normal operational capacity.

What security concerns should be addressed in API testing?

Security concerns include authentication and authorization, data encryption, input validation, and rate limiting. Authentication and authorization ensure only authorized users can access the API. Data encryption protects sensitive data during transmission. Input validation prevents injection attacks by validating inputs. Rate limiting ensures the API can handle misuse or abuse by limiting the number of requests a user can make.

Why is API documentation important in API testing?

API documentation is critical because it provides developers with the necessary information to understand and use the API effectively. Good documentation helps in understanding API capabilities, offering examples and guidelines on how to test various endpoints, and assisting in troubleshooting to diagnose and fix issues quickly.

What are some common challenges in API testing?

Common challenges include environment configuration, test data management, handling dependencies, versioning, and error handling. Environment configuration involves setting up the right environment for testing. Test data management ensures the availability of appropriate test data. Handling dependencies involves managing dependencies between different APIs. Versioning deals with different versions of the API. Error handling involves properly handling and testing for various error scenarios.

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