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Josh Grant 3 min read

How to Test a Java Application

Creating effective test cases and the right testing strategy for Java applications can be a time-consuming and complex task. This is where specialized testing solutions come in. With the right setup, developers can catch bugs early in the development process, before they become more difficult and expensive to fix. 

Additionally, testing methods can help identify and mitigate security vulnerabilities, which is critical for protecting sensitive data and maintaining the integrity of the application. In this blog, we will explore the different testing solutions available for Java applications. We will also discuss best practices for implementation, and how to choose the right testing solution for your specific needs.


Unit Testing for Java

Unit testing is a method of testing individual software units, e.g., by testing public methods from a given class. It is mainly used for functional tests. Most unit tests use predefined inputs to execute the functions of the system under test and observe the outputs and behavior to determine if the test passes or fails. However, creating test cases for unit tests manually can be time-consuming and not always accurate. When writing unit tests, it is important to focus on the individual unit and test its functionality in isolation.

This helps to ensure that any errors found are specific to the unit being tested, rather than a result of interactions with other parts of the system. Additionally, unit tests should be repeatable and reliable, providing consistent results each time they are run. One of the main benefits of unit testing is that it can be automated, to allow developers to catch bugs early in the development process before they become more difficult and expensive to fix.

Static Application Security Testing for Java (SAST)

SAST is a method of analyzing the underlying framework of the software under test by scanning it without executing it. This white-box testing approach requires access to the source code. Due to the lack of runtime context, SAST produces many false-positive test results that need to be sorted out manually. To combat this, SAST is often used in conjunction with specialized tools that can analyze the structure of Java applications and detect runtime errors. SAST tools can identify potential security vulnerabilities by analyzing the source code and identifying areas of the application that may be susceptible to attack.

Dynamic Application Security Testing for Java (DAST)

DAST is a method of testing software by feeding randomized or predefined test inputs into the system to trigger faulty program states. DAST is often conducted as a black-box testing method by security engineers and does not require access to the source code. DAST is useful for testing software from the attacker's perspective, by simulating real-world attacks on the application. This includes things like probing for vulnerabilities, attempting to bypass authentication, and attempting to access sensitive data. DAST is typically conducted after the application has been deployed, and can provide valuable information about how the application behaves when under attack. By identifying vulnerabilities and potential attack vectors, DAST can help developers take steps to improve the security of their applications.

Fuzz Testing for Java

Fuzz testing is an increasingly popular solution for Java testing that generates test inputs at random or based on information about the software under test. This usually means that a fuzzer generates test inputs based on information about code coverage which it then uses to uncover unusual or interesting program states that might expose an application to security or functional issues.

Fuzz testing is best applied as a method for continuous software security testing, starting in the early stages of development. Many modern fuzzing platforms offer CI/CD integration, allowing developers to quickly fix bugs and speed up development. Fuzz testing can be used to uncover a wide range of vulnerabilities, including buffer overflows, memory leaks, and logic errors. The randomized nature of fuzz testing makes it particularly effective at uncovering subtle bugs that might be difficult to find using other testing methods.

How We Found an XSS in a Popular Java Library Using Fuzzing (JSON Sanitizer)

If you are interested in finding out more about how fuzz testing can help to find bugs and vulnerabilities in Java applications, check out our best practices for Java testing. On this page, we gathered best practices for Java testing and a code example that details how we uncovered a Cross-Site Scripting vulnerability (XSS) in the JSON sanitizer library, using the open-source fuzzer Jazzer.