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What is API Testing: Understanding the Importance and Challenges

Updated Date: Sep 5, 2024
Guide to API Testing

Quick Summary: With the expanding use of APIs, testing becomes an essential approach to ensure that they meet the required expectations. API testing is an important process that helps to evaluate its quality. In this article, you will understand everything about API testing, its advantages, challenges, and the best practices to perform the testing.

APIs or Application Programming Interfaces help two systems communicate and are widely used in developing a myriad of applications. The importance of APIs is increasing with the rise of the API-first approach to developing applications and software. APIs have become cornerstones for modern enterprise applications. According to Businesswire, 97% of enterprise leaders have a belief that APIs are crucial for their survival.

While APIs facilitate communication between two or more disparate systems, testing becomes a critical aspect of building secure, performant, and reliable solutions. API security testing is an evaluation process that enables a tester to verify that the API is doing what it is designed to do. Testing APIs can be challenging when not done properly and leads to unexpected results.

This detailed guide on API testing will help you understand this concept, and its benefits, and look at the different types of API testing.

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Table of Contents
  1. What Does API Testing Mean?
  2. An Overview of the Different Types of API Testing
  3. Understanding the Importance of API Testing
  4. Key Advantages of API Testing
  5. Common Bugs That API Testing Detects
  6. What are the Challenges in API Testing?
  7. API Testing Best Practices
  8. To Wrap Up

What Does API Testing Mean?

API testing is a process of validating the behavior of an API by sending inputs (requests) and observing results (responses). The process aims to evaluate an API for performance, functionality, reliability, and security. API testing is crucial to verify that it is working as expected and there are no vulnerabilities that could lead to cyberattacks.

Today, layered architecture is dominating in application development which is divided into separate business logic, database, and presentation layers. Different APIs play a crucial role in the functioning of applications from taking user inputs, fetching, data, and processing logic, to sending results back to the user. Testing APIs ensure that the functionality of an application programming interface is seamless.

An Overview of the Different Types of API Testing

There are many types of tests performed on APIs as mentioned below.

Different Types of API Testing

Security Testing

It is a kind of testing that ensures that API endpoints are safe from attackers. API security testing is crucial to identify any defects or vulnerabilities that an attacker can exploit for malicious purposes. This process includes using an API scanning tool to perform several security checks like access control, authentication validation, encryption, and more to ensure API implementation is secure from external threats. Since APIs open communication with several systems, a single vulnerability can cause serious consequences.

Functional Testing

This test is performed to validate the functionality of an API. It works by feeding the API with the requisite payload or input and evaluating the results. The purpose of this testing is to ensure that API meets the functional requirements, business goals, and works in the specified hardware and software conditions. All in all, functioning testing determines the API’s functionality in real-world scenarios.

Load Testing

It evaluates the load capacity of an API to check how much traffic or calls the API can handle. API load test helps to determine how many concurrent users it can handle at a time. For this, API is bombarded with lots of traffic through emulated calls to verify its load-handling capacity. Load testing helps to identify performance bottlenecks. Either a specific unit or the entire code is tested with a gradual increase in traffic.

Fuzz Testing

It is a subgroup of security testing that aims to test API’s resilience. In this type of testing, an API is forced with a huge amount of random data to advertently cause crashes, failure, or negative behavior. It helps to test the API for the worst-case scenario. Fuzz testing helps to determine the absolute limit of the API.

Penetration Testing

It is another subgroup of security testing that attempts to detect vulnerabilities that attackers can exploit. Penetration testing works with simulated cyberattacks and evaluates API from outside. With APIs open to different inputs, they are prone to injection attacks that penetration tests can detect.

Runtime and Error Testing

These tests are performed when an API is actually running and monitor it. The tests help to detect execution errors, resource leaks, and other errors at runtime.

Validation Testing

This is the test that is performed at the final stage of a development process, but it’s very important. Validation testing helps to determine whether the API meets the planned objectives. This test corresponds to user acceptance testing. It validates the API, its behavior, and its efficiency. Does the API solve the problem described? Does the API use the right methods to access data? Is the API the most effective and efficient way to do the task? These are some questions that you need to answer to proceed.

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Understanding the Importance of API Testing

APIs are ubiquitous today because they connect different systems or applications with each other and build solutions faster. High competition and increasing user expectations put enormous pressure on businesses to keep their applications fast, error-free, and user-friendly.

Issues on the API layer can result in poor application performance and experience that leads to churn, negative impact on your business, and eroded user trust. So, the development team needs to deliver APIs that are highly performant and consistent.

API-first development has become commonplace among businesses where applications are divided into components known as services and connected via APIs. For this scenario, testing and validation are vital to ensure an API’s functionality, performance, security, and reliability.

Apart from this, there are lots of benefits of API testing that provide greater value to you. Let’s check the benefits below.

Save Time

API testing can be performed early in the application development cycle because it doesn’t require UI. It is possible to get quick test results with the use of automated testing that accelerates overall development workflow. Testing APIs quickly will help you concentrate on other core aspects of your application.

Cost Effective

It is one of those API testing advantages that has a wider aspect. Reduced costs in API testing will result in a decrease in overall application development costs. Since APIs can be tested earlier than the creation of the application’s UI and logic, many errors and bugs can be caught early. Identifying issues at the early stage will make bug fixing less expensive and easier later.

No Language Dependency

API testing is not dependent on any programming language or technology because data exchange occurs in XML or JSON format. Further, this communication uses compromised HTTP requests and responses. So, quality engineers can choose any programming language they like to perform API testing like JavaScript, Java, Python, etc.

Greater Testing Coverage

Automated API tests offer granular-level testing of your application. Further, it also covers many different test cases like functional and non-functional. API testing also requires running negative and positive tests. It ensures that every component is functioning as intended. So, testing your API covers a wider scope and helps to find defects in a larger scenario.

Shift Left Testing

API testing offers the benefits of shift-left testing because testing APIs take much less time than UI tests. So, testers can perform API testing quickly and early in the development pipeline. It contributes to the shift left approach to security testing which emphasizes that testing should be performed in the early stages of the development cycle.

Stable Testing

APIs are stable and they don’t require frequent changes like UIs. Further, APIs have comprehensive documentation where changes are also included to help engineers align their testing process. It results in more stable and easier API testing.

Key Advantages of API Testing

API testing is a crucial process that is generally conducted before deployment. Why is API testing necessary to conduct is something you know. But what benefits it offers is something you must be aware of. Check out API testing advantages.

Detection of Security Flaws at Initial Level

Since you conduct API testing, you can identify and fix security flaws at an initial stage in the development cycle. This early detection of vulnerabilities will enable businesses to fix them before they start affecting the system.

Better Coverage

API testing can provide more comprehensive coverage compared to UI testing. It can test functionalities and interactions that might be tough to reach or test manually through the user interface.

Improved Integration

Testing APIs helps businesses ensure that different devices and systems seamlessly interact. It allows businesses to verify that the integrated components function as per the requirements.

Security Validation

API testing ensures validating API endpoint security and data integrity by conducting various comprehensive security checks that ensure the system is protected from unauthorized access.

Automation Friendly

APIs are well-suited for automation, which means they allow organizations to conduct tests frequently and consistently without requiring significant manual intervention.

Documentation and Validation

Extensive API tests serve as living documentation that enables organizations to understand how multiple parts of the system interact and ensure that API documentation is accurate and up to date.

Common Bugs That API Testing Detects

Deployment of APIs without a thorough testing process can introduce many potential vulnerabilities and risks to your system. Therefore, conducting API testing is indispensable. Check out the critical bugs that the API testing detects.

Incorrect Response Codes

Detection: By sending requests to API endpoints and checking if the returned status codes match according to the API documentation.

Identified Bugs: Mismatched status codes like `404 Not Found` instead of `200 OK` or `500 Internal Server Error` instead of `400 Bad Request`.

Data Mismatch

Detection: Evaluating data differences by comparing actual data returned by the API against the standard data structure and content, as stated in the API documentation.

Identified Bugs: Missing fields, incorrect data types, or unexpected values in the API response.

Broken Endpoints

Detection: By testing each and every endpoint to ensure it responds correctly and performs the required function, such as retrieving or updating data.

Identified Bugs: Endpoints that fail to return the expected results or that produce errors when accessed.

Authentication and Authorization Issues

Detection: By testing APIs with multiple credentials and permissions to verify that only authorized users are accessible to it.

Identified Bugs: Issues where users can access restricted resources or perform actions they shouldn't be otherwise allowed to.

Concurrency Issues

Detection: By imitating multiple simultaneous requests to check how the API manages concurrent operations.

Identified Bugs: Problems like data corruption, race conditions, or abnormal behavior when various requests are processed at the same time.

What are the Challenges in API Testing?

API testing helps you ensure its quality and performance. However, there are a few challenges in API that make it difficult to maintain quality and reliability. Knowing these challenges will help make a better API testing strategy.

  • Testing APIs can be challenging due to the complex data formats they use. Parsing and validating data can be difficult.
  • Changing API functionality makes testing more difficult. Testers will need to change their testing approach in this scenario.
  • APIs may require specific configurations in different environments making testing difficult in those environments.
  • Testing APIs with authentication and authorization is more challenging because testers need to put extra effort into ensuring that the mechanism is implemented properly.
  • In case of limited documentation, testing an API can be very difficult. Testers will need more time to understand the documentation.

API Testing Best Practices

Testing your API is vital to ensure its quality and reliability. So, you must choose the right method to test your API. Following the best API testing practices will help you perform testing more accurately regardless of what API testing approach you follow.

  • Test Early and Test More: Incorporating API testing early in the development process helps you catch possible errors and issues at the earliest stage. Plus performing testing more often to minimize issues in the final stage.
  • Use a Dedicated Environment: You should create a testing environment that resembles the production environment for API testing. It helps the testing team to avoid user-facing downtime and handle issues.
  • Use Automated Testing: You can reduce the risks of human error by adopting testing automation. Today, automation is playing an important role in testing APIs that offer faster and reduce errors.
  • Leverage a Mock Service: You can leverage a mock API testing server when other APIs are not available.
  • Team Collaboration: Close collaboration between developers, testers, and other stockholders ensures quality testing.

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To Wrap Up

API tests are essential to ensure the quality and efficient data processing of any application. As APIs are vital for modern applications, ensuring they work flawlessly in real-world scenarios is essential. Hence, testing is not a choice, it’s a necessity. Automated testing can help you test APIs more quickly and simplify the process. Dynamic application security testing (DAST) is an efficient way to identify security flaws and improve security by working on them.

DAST is an automated approach to security testing that helps to identify potential vulnerabilities in APIs from outside. You can leverage a DAST tool like ZeroThreat to scan your API and discover potential weaknesses in minutes that could lead to security compromises. It is a trusted DAST API testing tool that makes testing exceptionally simple. It runs fast scans without compromising the accuracy and efficacy of tests.

Frequently Asked Questions

What is the relationship between API testing and API monitoring?

API testing checks the functionality and performance of APIs before deployment, whereas API monitoring consistently evaluates the API's performance in real time during its operation. API testing ensures capturing issues before the API's deployment, and monitoring ensures ongoing reliability and performance.

What is the future of API testing?

What are the top API testing tools?

What are the top methods of API testing?