API testing Tutorial
Tags: api, testing, beginners, tutorial
Published: 2023-10-11 10:56:41

API (Application Programming Interface) testing is a crucial skill for software professionals. Whether you’re new to testing or an experienced pro, this blog is your go-to resource.

We’ve distilled valuable insights from The Test Tribe’s 4th Virtual Meetup on API Testing with Pricilia into an easy-to-understand blog guide. For the visual learners out there, you can watch the complete video below.

Let’s explore the fundamentals of API testing, discover its various types, and learn best practices that will enhance your testing expertise. In this blog post, we will cover the API testing basics. Let’s dive right in!

## What is an API?

API is an acronym, and it stands for Application Programming Interface. API is a set of routines, protocols, and tools for building Software Applications. APIs specify how one software program should interact with other software programs. Normally, API facilitates the reusability.

**For example:**

If a user needs to book a room in Hyatt Regency. The user can directly do it on Hyatt Regency website, or through travel booking websites like MakeMyTrip, Trivago, etc.. So, here the Hyatt Regency develops an API and provides specific(read/write) access to the travel agencies via which users can view/book their hotels.

## Common Types of API

![Common Types of API](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ic8ydr1wmr8zdhue7ulr.png)
Various types of APIs serve distinct purposes, each with its own advantages and drawbacks. The most prevalent API categories include:

**Open API (Public API):**
These APIs are accessible to all developers and users. They typically have minimal authentication and authorization measures and may limit the data they provide. Some open APIs are free, while others require a subscription fee based on usage.

**Private API (Internal API):**
Intended solely for internal use within an organization, private APIs remain inaccessible to the general public. They often employ stricter authentication and authorization protocols, granting access to an organization’s internal data and systems for its employees or trusted partners.

**Partner API:**
Partner APIs are shared exclusively between strategic business partners. These APIs are not open to the general public and require specific permissions for access. They facilitate business-to-business activities, often involving the exchange of sensitive data, and typically employ robust authentication, authorization, and security measures.

## Understanding the Client-Server Architecture

![API Client-Server Architecture](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/wetiyjvxu6imsengu9ex.png)
Client-server architecture in API testing, within the context of a three-tier architecture, involves the interaction between different components for efficient and organized testing. Here’s an overview of this concept:

**1. Presentation Tier (Client):**
In API testing, the client or presentation tier represents the front-end or user interface through which users interact with an application.
Testers may simulate user actions and interactions with the client interface, such as making HTTP requests to the API endpoints.
The focus is on ensuring that the client can effectively communicate with the API and process the responses.

**2. Application Tier (Server):**
In the context of API testing, the server or application tier is where the API resides.
This tier handles incoming requests from clients, processes them, and provides responses.
Testers conduct various API tests here, including functional testing to validate the API’s behavior, performance testing to assess its responsiveness under load, and security testing to identify vulnerabilities.

**3. Data Tier (Database):**
In a three-tier architecture, the data tier, or database, stores and manages the application’s data.
While API testing primarily focuses on the interaction between the client and server, it’s important to verify that the API correctly accesses and manipulates data in the database.
Testers may perform database-related tests, such as data integrity checks and data consistency validation.

## What is API Testing?

API testing is a critical process in software testing that focuses on evaluating the functionality, performance, and reliability of an Application Programming Interface (API). It involves testing the API’s endpoints, request-response mechanisms, and data exchanges.

## Process Used in API Testing

![API testing Process](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/w0hlauwt68y37d9r52uk.png)
Here’s a detailed explanation of the API testing process outlined:

**1. Review and Understanding of API Specifications**
Begin by thoroughly reviewing the API documentation and specifications. This step ensures that testers have a clear understanding of what the API is designed to do, its endpoints, input parameters, and expected output.

**2. Categorize Entities Based on Flow**
Categorize the various entities, such as endpoints, methods, and data flows, based on the API’s functionality. This categorization helps in organizing test scenarios effectively.

**3. Define the Parameters**
Identify and define the parameters required for each API endpoint. Parameters include inputs, headers, query parameters, and authentication details. Ensure that you understand the purpose of each parameter.

**4. Learn How to Send Requests for Different Endpoints**
Familiarize yourself with the tools and methods for sending requests to the API endpoints. This may involve using API testing tools, command-line tools, or scripting in a programming language.

**5. Frame the Test Cases**
Create comprehensive test cases for each API endpoint. Test cases should cover various scenarios, including valid and invalid inputs, boundary cases, and edge cases. Define the expected outcomes for each test case.

**6. Add Assertions on the Expected Results**
Define assertions to validate the API responses. Assertions are criteria that must be met for a test case to pass. They can include checking response status codes, data integrity, and expected values.

**7. Test Execution**
Execute the test cases against the API endpoints. Ensure that you follow a systematic approach, covering all defined scenarios. This phase involves sending requests, receiving responses, and comparing the actual outcomes to the expected results.

**8. Report the Failure**
If a test case fails, document the failure with as much detail as possible. Include information about the test environment, input data, and any error messages or unexpected behavior encountered during testing.

## Why is API Testing Done?

![Why is API Testing Done?](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/hmojzqn6qmzkbnoukbnx.png)
In the ever-evolving realm of software development, ensuring the reliability and efficiency of applications has never been more crucial. This is where API testing steps into the spotlight as a game-changer. In this, we explore the compelling reasons why API testing should be an integral part of your testing strategy.

**1. Time Efficiency**
First and foremost, API testing is a time-saver. Traditional testing methods often involve testing the entire application, which can be time-consuming, especially in complex systems. API testing, on the other hand, allows testers to focus on specific functionalities or endpoints. This targeted approach significantly reduces testing time, allowing for quicker development cycles and faster time-to-market.

**2. Cost Reduction**
In the world of software development, time is money. By accelerating the testing process and streamlining it with API testing, you’re effectively reducing testing costs. With fewer resources required for testing, your organization can allocate resources more efficiently and effectively, ultimately saving valuable budgetary resources.

**3. Language Independence**
API testing breaks down language barriers. Unlike some testing methods that depend on specific programming languages or technologies, API testing is language-independent. This means you can test APIs built with different technologies or languages without the need for a deep understanding of each language. This flexibility is a significant advantage in today’s multilingual software landscape.

**4. Core Functionality Testing**
At the heart of every software application lies its core functionality. API testing specializes in scrutinizing this essential aspect. It allows you to dive deep into the core of your application, testing how its various components interact and ensuring that they perform as expected. This pinpoint accuracy in testing core functions enhances the overall quality of your software.

**5. Risk Mitigation**
Software development inherently carries risks. API testing acts as a risk mitigation tool. By thoroughly testing APIs before integrating them into the application, you can identify and address potential issues and vulnerabilities early in the development cycle. This proactive approach reduces the likelihood of critical failures in the production environment, ultimately safeguarding your system’s integrity.

## Types of API Testing

![Types of API Testing](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/5y2ewniad11fo4jvucid.png)
APIs (Application Programming Interfaces) are the backbone of modern software, enabling seamless communication between applications and services. To ensure that APIs perform flawlessly and securely, API testing comes into play. Let’s take a closer look at the various types of API testing and their distinct roles in the software testing ecosystem.

**1. Validational API Testing**
Validational API testing, also known as Schema Testing, focuses on verifying that the API responses adhere to the expected data format and structure. This type of testing ensures that the data exchanged between the API and the application is correctly formatted, preventing potential data-related issues.

**2. Functional API Testing**
Functional API testing is all about functionality. It verifies whether the API functions as intended by testing its various endpoints and methods. Testers create test cases to assess the API’s behavior, input validation, and output correctness. This type of testing is critical for confirming that the API delivers the expected results under various scenarios.

**3. Security API Testing**
In an age where cybersecurity is paramount, Security API Testing is indispensable. It involves scrutinizing the API for vulnerabilities and security flaws. This testing type assesses the API’s ability to protect sensitive data, prevent unauthorized access, and resist common security threats like SQL injection or cross-site scripting (XSS) attacks.

**4. Load API Testing**
Load API testing assesses how well the API performs under different levels of load and stress. It helps determine the API’s capacity to handle concurrent requests and large volumes of data. By simulating heavy loads, testers can identify performance bottlenecks and ensure the API remains responsive and reliable in real-world scenarios.

**5. Integration API Testing**
Integration API testing evaluates how well the API interacts with other systems and services within an application’s ecosystem. It ensures seamless communication between various components, detecting integration issues that could disrupt the overall functionality of the application.

**6. Documentation API Testing**
API documentation is the user manual for developers and users who interact with your API. Documentation API testing validates that the documentation accurately represents the API’s behavior. It confirms that developers can rely on the documentation to understand how to use the API effectively.

This post is an excerpt from the 4th virtual Meetup by The Test Tribe with Pricilla Belwin. Head over to the website for a comprehensive guide on [API Testing Tutorial for Complete Beginners](https://www.thetesttribe.com/blog/api-testing-tutorial-for-beginners/)