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API Testing Guide for Beginners: What do you need to know?

Published on 23 October 20

Developers who test application programming interfaces are testing software that performs direct verification at the API level. The integration testing determines whether an API meets the required expectations for things like reliability, functionality, performance, and security. If you are new to testing APIs, here is an excellent overview of the key things you need to know.

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Understanding the Purpose of the API

By knowing the purpose of the API you test, you can prepare your test data input and output accordingly. Knowing the purpose also enables you to define your verification approach. For instance, you may need to verify the API’s responses against the database, or you may need to verify the responses against other APIs.

Selecting a Suitable Automation Tool

To ensure you leverage the automation capabilities of testing APIs, you need to choose the most suitable tools. Hundreds of testing software are available, so spend some time comparing them to find the right one for your task. Some of the best API testing tools on the market are RapidAPI, Paw, and REST-assured.

How to Classify Status Codes

API response status codes are categorized into five global-standard classes. The status code’s first digit defines the response class, whereas the last two digits do not refer to any class. The first digit can be one of five values. They are:

  • 1xx, which indicates an informational request has been received and is continuing to be processed.
  • 2xx, which indicates a request has been received, understood, and accepted successfully.
  • 3xx, which indicates redirection, meaning further action is required to complete the request.
  • 4xx, which indicates a client error, meaning the request contains the wrong syntax and, therefore, cannot be fulfilled.
  • 5xx, which indicates a server error.

How to Organize API Endpoints

When you begin working on a testing project, you could have hundreds of APIs to test, so it is best to organize them into categories. That will help you to create testing scenarios with high coverage and integration. By organizing tests with the same structures, such as resource type and path, you can reuse tests and make them extendable with integration flow.

Choosing the Right Verification Methods

It is essential you select a suitable verification method for a given API. The response status code informs you of a request’s status, and the response body content is what is returned from an API with the given input. Response content will vary depending on data types and sizes. Responses can be received in formats like plain text, an XML document, or a JSON data structure.

Performing Positive and Negative Tests

To ensure an API is working correctly, you will need to perform both positive and negative tests. Both tests are driven by input and output data. Positive tests include verifying that the API receives the input and output returns as expected and verifying that the response status code is returned as required. Negative testing includes verifying an API returns an appropriate response when the output is not as expected and performing validation tests.

Live Testing

It is best to schedule API tests every day while the testing process is live. Because API testing is quick and stable, it is simple to add more tests into the present testing process with minimal risk. However, that is only possible when your automated API testing tools include features such as test schedules with built-in commands, and integrated test management tools, and defect tracking tools.

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