What Is API Testing — A Definitive Guide

Application Programming Interface also called API is a conversation channel among different applications.Let’s understand this through an example of Traveller, Travel agent, and Tour Operator.

Step 1: The Traveller being the end user will communicate their travel requirements to the Travel Agent.

Step 2: The Travel Agent acting as an intermediary, collects the information from the Traveller and communicates it to the Tour Operator.

Step 3: The Tour Operator then creates and sends a travel package as per the requirements of the traveler to the Travel Agent. The Travel Agent then communicates the same to the Traveler.

Think of API as the communication channel. Just like how the Travel Agent interacts with the Tour Operator to gather information and provide the information to the Traveller, the APIs are like an invisible bridge that connects the two.

API enables the communication between the software applications using code based instructions. When it comes to developer point of view, the API documentation will provide the information on the application integration. APIs are the intermediate layer that helps in processing data and transferring it between systems and applications.

What is API testing?

To understand API testing, let’s first talk about SDLC — Software Development Life Cycle. In order to produce good quality software the engineering team will follow a set of step by step processes to ensure the quality and integrity of the software. SDLC usually consists of six steps: Planning, Defining, Designing, Building, Testing and Deployment.

When it comes to the Design phase in SDLC, it is all about software architecture. The software requires a stable architectural design to showcase the design and flow of the software.

It describes how each of the components in a software system are assembled, what is the relationship between them and how the communication flow happens. It shows the behavior of the software system and the significance of its elements.

Software testing is carried out to understand the behavior of the software, to evaluate if the software performs as expected. API testing is also a type of software testing, where we can either directly test individual APIs or its integrations. The APIs have to be tested for its functionality, reliability, performance and security.

API testing is an integral part of API development life cycle as it streamlines the business process in the software application. API testing is carried out by both developers and testers/QA experts. The developers usually check if the API follows the protocols and standards as documented, on the other hand testers have to check the API for its functionally, integrations and security to ensure that a quality software is delivered to the end user. API testing also ensures efficient software delivery.

Test case Development

• It involves the coding of test scenarios, where testers/QA team meticulously design and outline the steps to assess the functionality of a software application.
• Test case development extends to the creation of sanity check test suites, which are designed to quickly verify that basic functionalities work as expected after changes or updates.
• This is a comprehensive process that ensures the quality, functionality, and resilience of software applications, helping deliver a superior user experience.

Test Execution and Reporting

• During this phase, testing teams systematically run the test cases, applying various inputs and scenarios to evaluate the software’s performance, functionality, and compatibility.
• This rigorous examination ensures that the software meets the required standards and specifications.
• As the tests are executed, detailed records are maintained, documenting the results of each test case. These reports include information on test case status, any defects identified, and any deviations from expected outcomes.

API specification and Review

• API specification reviews are vital for ensuring the functionality, compatibility, and security of software interfaces.
• During these reviews, the team assesses the clarity and completeness of the API documentation, focusing on essential aspects like endpoint definitions, data formats, and authentication methods.
• They also scrutinize error handling procedures and compliance with industry standards to identify potential vulnerabilities.

Test Specification and Document

• During this stage, testers /QA team will define the scope, objectives, and criteria for testing. They outline the specific test cases, including inputs, expected outcomes, and the order of execution.
• They will also determine the test data and testing environments. Test specification development ensures a systematic and thorough approach to testing.

Test Framework development

• Involves creating a structured foundation for testing processes. This framework provides a set of rules, guidelines, and reusable components that streamline and standardize testing activities.
• It simplifies test case creation, execution, and reporting, enhancing efficiency and consistency across testing efforts.
• It plays a pivotal role in ensuring the reliability and quality of software by facilitating thorough and systematic testing practices.

How to approach API testing

It all starts by clearly defining the APIs scope and functionality, endpoints, expected responses in case of both correct and incorrect inputs. This is then followed by writing test cases specifying the conditions and variables to evaluate the APIs and its response to the given input. While writing the test cases the testing team makes sure to cover all factors like response time, the data quality, HTTP status codes and error handling.

The API testing process thoroughly examines various endpoints such as web services, database or web UI. The security and performance of the APIs are a vital aspect of the software. The testing team also ensures that the API functions correctly across different browsers and devices.

• A team of developers, testers, system architects and project managers will collaboratively write down the API requirements. Each stakeholder has to communicate their inputs clearly.
• The requirements will involve sorting out on the functions of the API, how the API will handle the data, what happens in case of unexpected input, what is the desired output, incase of failure how will the system handle it and many other important details required.
• The testing team will then test the APIs and its integration in various testing environments.
• All the details and processes are documented and reviewed.
• Once the API integrations are set up an end-to-end testing is carried out.
• Testing is done thoroughly to identify and fix bugs at the earliest as possible.

Benefits of API testing

Early Error Detection: A well structured API testing will enable early identification of errors in the application’s core functionality, it could be done much before the user interface is fully developed. It will help save time and resources.

Faster Release cycle: When compared to GUI (Graphical User Interface) testing, API testing usually allows faster releases, This provides time for development and testing teams to focus on other critical aspects of software development.

Test Coverage: API testing provides comprehensive coverage as it examines the underlying layers of the application and ensures if the databases and system components are communicating correctly. This leads to better software quality and better user experience.

Shift Left Testing: Developers can easily shift left by running API tests without the need for a graphical user interface (GUI). This provides a way for early testing and immediate feedback for faster error resolution. This indeed will help in reducing the chances of costly late-stage fixes.

Lower Maintenance: API tests focus primarily on major updates in business logic, which are typically well-documented. Therefore it is easy to maintain. API layers are less prone to subsequent regressions caused by recent merges or releases, reducing the need for ongoing maintenance.

Cost-Effective: As mentioned above, API testing is easier to maintain, and provides quick results, resulting in significantly reduced testing costs. Resources can be reallocated to other critical tasks, optimizing time, money, and effort.

Why Use API Testing — Pros and Cons

Pros of API testing:

Enhanced Functionality: API testing ensures if the API is performing as expected and provides guarantee on its accuracy and completeness when it comes to data exchange.

Security checks: API testing is done to make sure that the API is secured against common threats to safeguard sensitive data.

Optimized Performance: Testing APIs helps resolve bottleneck issues related to response time and error rates. It also ensures the API can handle expected loads for a seamless user experience.

Seamless Integration: The APIs are tested to verify that different application systems are working in an orderly manner to exchange accurate and secure data.

Risk Mitigation: Continuously testing at regular intervals significantly reduces the risk of system failure or poor performance of the system. It helps rectify the issues before deployment. This saves a lot of time and cost.

Cons of API testing

Limited User Interface Testing — API testing requires a certain level of experience to avoid confusions for testers while setting up the test environment, or automating the scripts. Since testing APIs primarily focuses on data and functionality validation at the backend it might not cover the user interface aspects.

UI Validation: Based on the above mentioned point , it becomes necessary to validate UI to guarantee that users can interact with the expectation as expected. This makes it necessary to perform both API and UI testing.

Dependence on documentation: To set up API process flow to make sure it performs effectively, it requires heavy documentation. The documentation process has to be accurate and up-to-date.

Time Investment: The initial set of the APIs and writing accurate documentation for the same requires time investment and skilled resources.

API Testing Tools

Testsigma

Testsigma’s API testing platform helps in building API tests and validating the responses in real-time. It also improves test converge by integrating the API tests with functional tests. Another big highlight is that you need not have prior coding knowledge to write test cases in Testsigma, this platform lets you write test cases using NLPs (Natural Language Processing).Reusable components can be created and it also helps automate the most complex API workflows.

Recently, Testsigma has also made it easier to import a postman API collection, all that has to be done is to export the Postman collection and environments as a JSON or ZIP file and then upload it into Testsigma platform and perform the required testing. It also allows you to customize the imported Postman Collections and add additional test steps as required.

You can store parameters as data profiles and verify multiple scenarios while testing APIs with multiple test data sets without making script changes every single time. Validation of API is made flexible, it can be done by choosing between various schema modes in order to compare actual response values with the expected responses. It helps gain control and better flexibility over the tests by automatically capturing the specific run time data from the API responses and reusing it in the subsequent tests. This tool also has a Open Source version, Pro plan for fast growing teams and enterprise plan for large teams.

Postman:

Postman’s API builder simplifies the API lifecycle from design to deployment and integration. It also has integration with git that can automatically synchronize API documentation making work much easier for developers. Postman API platform offers free and different pricing structures tailored to different users’ needs. When it comes to API test automation Postman provides local collection runner, Local performance testing and monitoring calls and mock servers calls on a monthly basis. Postman also provides API tooling, workspace collaboration, Internal API management and much more.

Katalon:

Katalon has both free and flexible paid plans for users to meet their requirements. It requires minimal maintenance. It uses docker containers for easy deployment and also provides real-time analytics for both local and remote executions. Katalon works with modern frameworks and supports BDD with Cucumber files and native Gherkin editor. It is API centric and supports all types of Soap/1.1, Soap/1.2 and REST requests. Tests can also be imported from Swagger, Postman and WSDL.

SoapUI

SoupUI supported by smartbear has both an open source version and commercial tool for API testing. This testing tool helps in creating, managing and executing end-to-end tests on REST, SOAP & GraphQL APIs, JMS, JDBC and other web services easier. Thus ensuring faster delivery of softwares. It also has a Ready API, which is a suite consisting of tools in order to ensure high quality, good performance and strong security in the APIs. It provides API security testing, performance testing and speed testing at scale.

Swagger.io

The SwaggerHub Explore is available for both teams and for enterprises. It helps in exploring and quickly validating the functionalities of an API. The documentation process is made simple to help teams understand the APIs before its implementation. It enables users in analyzing the API data received from a request to easily evaluating the APIs. The tool is designed in a way that it is easy to use to discover, understand and integrate multi-protocol APIs.

Conclusion

By now it is understood that API testing is an important part of software development and quality assurance. The holistic approach is to perform both API and User Interface testing to get to the fullest potential of API testing and deliver an excellent user experience.

As technology continues to advance, API testing plays a vital role towards building a software with strong integrity and ensuring the software systems for optimized performance.