Web Design

Role of API in Performance Testing: 6 Important Points To Remember


A software application has three architectural layers: the presentation, business logic, and database layers. The business logic layer is the most important part of an application because it receives data input from users via the presentation layer, queries the database layer, processes the data, and presents it as output to the user via the presentation layer. It also interacts with other application layers using an Application Programming Interface (API), without which it wouldn’t be able to perform the functions stated above.

Therefore, an API determines an application’s uses and functionalities; hence it is important to test an application’s API to verify that its Business logic layer performs as intended.

In this article, you will learn about API testing and its importance.

What is API testing?

Let’s start by understanding what is end to end testing, how it functions and what role does it play. This tests an application’s API performance to ensure that the API behaves as intended. API testing tests an application’s functionality, security, and reliability, ensuring that the application runs as intended; hence, it is a mandatory automation test for an application in its developmental stages.

Benefits of API Performance Testing

  1. API testing ensures that your API performs as intended, giving back the expected data output based on parameters.
  2. An application’s core functionalities and performance can be tested for errors and inconsistencies using API testing while in its developmental stage. Undetected bugs in a software’s API can cost much, delay product release, and make clients lose their trust in the product.
  3. API testing is simulating how end-users will interact with the software application in the real world.
  4. With API testing, finding and fixing inconsistencies in a program’s software code is quicker than UI tests. Results from Andersen lab show that running an API test is about 33 times faster than a UI test.
  5. API testing ensures the integrity of boundary conditions and positive/negative testing.
  6. Unlike unit tests designed to test the functionality of an application’s component singly, API testing is a broader test that tests the performance of an application’s component collectively, ensuring that they perform as intended.

In summary, API testing ensures that:

  • An application performs its purpose for its creation
  • The application has the requirement to handle the load
  • Developers can find inconsistencies that can be costly to adjust after the product is released into the market.
  • The application runs on multiple platforms and devices.

Types of API testing

1. API Functional testing

API Functional test verifies that the API is doing exactly what it needs to do.

2. API Reliability testing

API Reliability testing tests the API’s ability to connect and interact seamlessly with other applications and end-users.

3. API Load testing

API Load testing verifies that the API can handle many calls (data input).

4. API Creativity testing

This test proves that the API can endure different use cases depending on users’ interaction with the application.

5. API Security testing

API Security testing ensures that the API meets all security specifications like authentication, access controls, and permissions.

6. Negative testing

Negative testing simulates users’ interaction with the API using valid and invalid data input for prohibited operations.

6 Points to remember

1. Understand the purpose of the API

Before carrying out an API test, you need to review the API, understand its purpose and how it works, and know the expected output. E.g., when carrying out an HTTP API test, you should understand the OpenAPI specification, which details an HTTP API’s standard, values, objects, and parameters, how it calls objects, the object’s purpose and uses, etc.

2. Know the API testing requirements

You should know the API’s testing requirements, including the application’s workflow, features and functionalities, inconsistencies you’re checking for, expected output, and the target market. E.g., you may want to verify that your HTTP API is receiving expected responses within the specified timeframe stated in the test plan.

3. Define the API’s input parameter

Input parameters are the specified data input needed by an API to function. Before starting an API test, you must define your input parameters to determine if an API is performing as expected. E.g., you may need to set input values for your headers, queries, parameters, etc., for a REST API.

4. Run a Positive and Negative API testing

Running positive and negative API testing determines whether an API is functioning as expected. A positive test verifies that an API is performing its expected purpose, while a negative test verifies an API’s response to using valid or invalid data for voided operations. E.g., inputting an existing or non-existing username.

5. Organize API endpoints

If you’re running multiple API tests, you should organize the APIs into categories to help create and manage test scenarios.

6. Choose a suitable API test automation tool

Before choosing an API test automation tool, you must consider the following:

  • Your budget
  • API type
  • Choice of API test you will be running.

Below is a suggestion of some of the best API testing automation tools

  • SoapUI
  • Postman
  • Tricentis Tosca
  • Katalon Studio
  • Mocklets
  • Apache JMeter
  • Rest Assured
  • SmartBear

Final Thoughts

An application’s API performance determines how well it is accepted by intended consumers. Therefore, ensuring product success starts by getting it right with your API by using the right API test tool to ensure that your product application performs as expected, is free from bugs, enjoys early market release, and guarantees customer satisfaction.