API Functional Testing | Verify your API's Abilities

API functional testing verifies the core functionalities of an application's engine (the API) by simulating various data requests and examining responses. It ensures the API behaves as expected under different conditions, delivering the right data and handling errors gracefully.

Steven Ang Cheong Seng

Steven Ang Cheong Seng

15 May 2025

API Functional Testing | Verify your API's Abilities

APIs (Application Programming Interfaces) will always have to undergo some form of testing before they can be released for consumption. An API has to be able to perform the functionalities they are intended to do - else, they become useless! One of the methods to ensure that APIs are working properly is API functional testing.

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Apidog can help with various forms of testing with its flexible testing features. With Apidog, you can test API endpoints individually, or run multiple-step test cases called test scenarios to mimic real-world situations!

Since Apidog is free, give the API platform a try by clicking on the button below! 👇 👇 👇
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What is API Functional Testing?

API functional testing is a niche type of testing that verifies the functionalities of an API. It is to ensure that the API works as intended under various conditions.

API functional testing may differ from other forms of software testing, as you can immediately connect with the API through PAI tools or pure computing coding.

What Constitutes an API Functional Test?

1. Scenario:  Each test focuses on a specific scenario that simulates a real-world interaction with the API. This scenario could involve:

2. Assertions:  These are statements that define the expected outcome of the test. After simulating the request, the API's response is compared against these assertions. Common assertions include:

Types of API Functional Tests

1.Positive Tests

Positive tests simulate ideal user interactions with the API. They focus on scenarios where everything goes according to plan, ensuring the API processes valid data and delivers the expected results. Here's a closer look at what positive tests encompass:

2.Negative Tests

Negative tests, also known as error handling tests, explore how the API reacts to unexpected or invalid user input. They intentionally provide faulty data or perform actions that deviate from normal usage to assess the API's robustness. Here's what negative tests delve into:

Consequences of Skipping API Functional Testing

1. Integration Issues:

2. Unreliable Functionality:

3. Security Risks:

4. Development Challenges:

Apidog - Testing APIs via Endpoints or Testing Scenarios

Testing APIs are part of every API lifecycle, so it is an inevitable process that all API developers have to face. Testing APIs tends to also be the most tedious, as there are countless situations in which APIs can be situated.

To solve your API nightmares, you can consider using Apidog. Apidog provides API developers with an easy-to-understand API platform for testing APIs individually or in bulk.

apidog interface
Apidog An integrated platform for API design, debugging, development, mock, and testing
REAL API Design-first Development Platform. Design. Debug. Test. Document. Mock. Build APIs Faster & Together.
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Testing Individual API Endpoints Using Apidog

If you want to swiftly test a single API with Apidog, you can follow the steps below!

To target the correct API endpoint, you first have to insert the corresponding API endpoint that you want to test. Once you have included the intended API URL, include the parameters that you want to use for the endpoint (if relevant).

In case you are unfamiliar with passing multiple parameters in an API URL, check out this article to find out how you can specifically target a resource inside a rich collection of data!

Tutorial: How to Pass Multiple Parameters in REST API URLs?
Two commonly seen parameter types are widely used in modern websites. Although they slightly differ based on their functions, parameters help developers identify specific resources found within a collection or system.

Create Multiple-Step Testing Scenarios for Your API Using Apidog

If you need to simulate a real-world scenario, or just have multiple conditions that you want to test your API through, you can try to use Apidog's testing scenario feature.

initializing new test scenario apidog

Firstly, hit the Testing button, followed by the + New Test Scenario button.

add detail apidog test scenario

Apidog will prompt you to fill in the details for your new test scenario. Make sure to give it a proper name so its function is predictable.

add step new test scenario api apidog

Continue by adding a step (or many more steps) to your test scenarios by clicking on the Add Step section. You should be able to see the image below.

select import from api soap apidog

Select "Import from API" from the drop-down menu.

add soap api web service test case scenario apidog

Next, select all the APIs you would like to include in your test scenario. In the example above, the API called NumberConversionSOAP has been included.

edit testing environment start run test scenario apidog

Before hitting the Run button to start your test scenario, make sure to change the test scenario environment, which should be Testing Env, as pointed out by Arrow 1.

apidog testing scenario results

You can get a detailed analysis regarding your API(s) performance, seeing where they lack or excel. By knowing your APIs better, you can therefore assess what you need to do next in your next phase of API development.

Conclusion

API functional testing serves as a cornerstone for building reliable and well-integrated APIs. Simulating various user interactions and examining the API's responses ensures the API functions as intended under diverse conditions.

This proactive approach helps identify and rectify bugs early in the development process, preventing issues that could manifest later and disrupt dependent applications. In conclusion, investing in thorough API functional testing is an essential step toward ensuring the smooth operation and long-term success of any API-driven ecosystem.

If you wish to find an API tool that is compatible with many different API file types, you should strongly consider Apidog. With the many testing capabilities that Apidog facilitates, the API tool can reliably support any API developers journey to creating the best API.

Apidog An integrated platform for API design, debugging, development, mock, and testing
REAL API Design-first Development Platform. Design. Debug. Test. Document. Mock. Build APIs Faster & Together.
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