Get Started with API Testing

Mar 5, 2020 | Best Practices

api testing - the ugly duckling of testing

In recent years, the technological needs of consumers have exponentially increased, prompting companies to build applications that are more scalable, secure, multi-threaded, and faster to respond than ever before. To ensure all these attributes are present in the applications we all use, APIs were created to allow developers to tap into external programs instead of creating a new one from scratch.

APIs, or application programming interfaces, provide a level of abstraction by exposing only the data needed to communicate with another system. For example, Google’s Maps API is used by many organizations to provide Google Maps functionality, rather than companies building their own map applications. The same holds true for Mint, the finance application that connects to different banks via APIs to fetch required customer data.

The growth of new software development techniques like micro-services has served as a catalyst in the API movement by removing dependencies and establishing easier data exchange between different software components.

More often than not, organizations overlook testing APIs because they opt to focus on other aspects of the system, such as the UI, databases, application code, security, and performance. API testing is also bypassed because it is time-consuming and requires certain specialized skill sets, tools, and approaches.

But like the ugly duckling from Hans Christian Andersen’s timeless tale, API testing shouldn’t be overlooked. Organizations often fail to realize the critical importance of APIs and the impact of their failure in production.

Here are some different aspects of testing APIs and what to look for.

Develop an API Testing Strategy

Before diving into API testing, it’s crucial to craft a well-thought-out strategy. Consider these key questions to lay the groundwork for your testing efforts:

  • Public-Facing or Internal APIs: Identify whether your API will be used externally by partners or internally by different components of your system.
  • Target Audience: Understand the audience for your API and tailor your testing approach accordingly.
  • Integration Scope: Determine if your API needs to integrate with external systems or if it operates independently.
  • Endpoint and Value Types: Familiarize yourself with the various endpoints and data types involved in your API.
  • Data Source and Access: Explore where the data originates and whether specific authentication is required.
  • Expected Results and Scenarios: Plan how you will verify if the API performs as intended under different scenarios.

The 3 Aspects of API Testing

There are three major aspects to cover when performing API testing.


To test API connectivity, make a call to the API using its URL. If a 200 response is returned, the API is connected. If no response is returned or a connection failure error is returned, then connectivity failed, meaning the request was not received by the server.


All API calls return different status codes indicating what happened during the interaction. This serves as a reference to see whether the APIs are working as intended. The following are the main different status codes to pay attention to while doing API testing:

  • 400 BAD REQUEST: Generic error that is returned when no other 4xx status code is appropriate, such as for domain validation errors, missing data, or improper API requests.
  • 401 UNAUTHORIZED: Missing or invalid authentication token.
  • 403 FORBIDDEN: The user is not authorized to perform the operation.
  • 404 NOT FOUND: The requested resource is not found. It may not exist, or there may have been a 401 or 403 error and, for security reasons, the service masks it as a 404 error.
  • 409 CONFLICT: Resource conflicts, such as duplicate entries are found, or an attempt to delete root objects when cascade-delete is not supported.
  • 500 INTERNAL SERVER ERROR: General catch-all error when the server-side throws an exception, and the consumer cannot identify the exact error from their end.


An API’s performance can be its most valuable feature. Each time an API request is made, the response must be returned in a matter of milliseconds.

Depending on the application, thousands, if not millions, of API requests can be made at a time, as in the case of Facebook, Google, and Twitter. Therefore, APIs should be able to handle large amounts of load without failing. If the API does not have fast response times and is unable to handle large numbers of requests, it is essentially worthless.

Choose Your API Testing Tools

We are living in a world of APIs. Every second there are thousands of API calls happening in the back end without us even noticing it. Performing API testing is a critical part of the overall testing process, and it is about time we start paying attention to it.

Selecting the appropriate testing tools is crucial to the success of your API testing endeavors. With Ranorex, you have the flexibility to choose from a variety of standalone API testing tools or opt for a more integrated approach, combining API testing with other testing types.


Additional Strategies for API Testing

Want to up your API testing even further? Use it alongside the following best practices, including creating robust and maintainable API test suites, managing API versioning, and implementing data-driven testing for optimal efficiency.

  • Integrating API Testing with CI/CD: Automating API tests and incorporating them into your development workflow ensures early bug detection and a smoother release process.
  • Ensuring API Security and Performance Monitoring: Don’t forget about security testing for APIs. Check authorization, authentication, and safeguard sensitive data.
  • Continuous API Monitoring and Comprehensive Reporting: Keep an active pulse on what’s happening in real-time to avoid bottlenecks and ensure reliability.

Conclusion: Put API Testing in Focus

API testing is a critical aspect of the overall testing process, and we urge developers to embrace it wholeheartedly. By employing the right strategies, tools, and best practices, you can elevate the performance and reliability of your APIs, delivering exceptional experiences to your end-users.

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