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JUnit Automated Test Case Generation & Code Coverage

Headshot of Arthur Hicken, Evangelist at Parasoft
August 16, 2023
7 min read

Learn how to use Parasoft Jtest and Junit automated test case generation to accurately assess the code coverage of each test you run.

Having bugs in your code can result in dire consequences. That’s why quality-first companies don’t leave any stone unturned when it comes to ensuring the quality and reliability of their code. One way to ensure this is through unit testing, where developers verify that their code functions as intended and produces the expected results.

To streamline this process and improve efficiency, automated test case generation and code coverage analysis have emerged as valuable unit testing techniques. Teams can apply these techniques to JUnit tests using Parasoft Jtest, a popular developer productivity solution for Java applications that offers robust support for automated test case generation and code coverage analysis.

If code coverage is important to your team, then make sure you’re measuring it right and collecting data from all the tests you run. Leverage automatic JUnit test case generation to quickly build and expand your unit tests to get meaningful, maintainable test suites for high levels of code coverage.

The Importance of the JUnit Testing Framework in Software Development

The JUnit testing framework has become a standard in the Java development ecosystem. Here are some key reasons why the JUnit testing framework has become vital among software engineers.

Ensures Correctness and Reliability

The primary purpose of testing is to identify and remediate defects in software. JUnit plays a vital role in achieving this goal by providing a standardized framework for writing and running tests. Developers can create test cases that verify the correctness and expected behavior of individual units of code, such as methods and classes. These tests can be executed automatically, ensuring that software functions as intended and minimizing the probability of introducing new bugs during development or future modifications.

Code Maintainability

Writing tests with JUnit encourages developers to write modular, loosely coupled code that’s easier to maintain and refactor. By defining testable units and writing corresponding tests, developers are forced to think about the design and architecture of their code. This results in cleaner, more modular code that’s easier to understand, extend, and modify in the future.

Regression Testing

When adding new features or making changes to an existing code base, there’s always a risk of unintentionally breaking previously working functionality. JUnit provides a safety net by allowing developers to rerun tests after each change, ensuring the existing behavior remains intact. This helps catch regression bugs early and prevents the introduction of new issues.

Understanding JUnit Automated Test Generation

Automated testing has become an integral part of software development, allowing developers to ensure the quality and correctness of their code. JUnit, a widely used testing framework for Java applications, offers a powerful toolset for creating and executing tests. Although most software testers write unit tests manually, taking that approach can be time-consuming. Parasoft Jtest provides a better solution by incorporating automated test generation techniques.

Automated test generation refers to the process of automatically creating test cases based on specific criteria or properties of the code under test. This approach can help developers in the following ways.

  • Save time.
  • Improve test coverage.
  • Discover potential issues that might otherwise go unnoticed.
  • Achieve higher levels of code coverage by generating tests for use cases for which it might be impractical to manually create exhaustive tests.
  • Quickly create a set of tests for legacy code with too few (or no) tests, enabling development teams to work confidently on that code without fear of unknowingly breaking functionality.
  • Identify edge cases and unique scenarios that might be missed during manual test creation.

By exploring a wide range of inputs and scenarios, automated test generation processes can identify additional potential bugs and vulnerabilities through the tests they create.

How Parasoft Jtest Enhances JUnit

Parasoft Jtest uses and enhances the capabilities of JUnit with a full suite of test automation capabilities including test coverage and collaboration and documentation.

Test Coverage

Maintaining comprehensive test coverage is crucial for software quality. Parasoft Jtest measures the extent to which tests cover code, helping your team to identify areas where test cases are missing. With this knowledge, developers can write additional tests with Jtest’s assistance to increase coverage and improve confidence in the software’s reliability. Additionally, Jtest can capture coverage from other types of tests for a holistic view of code coverage that takes all your tests into account.

During code refactoring, Jtest provides immediate feedback on whether code modifications break existing functionality. This immediate feedback from automated regression tests means developers can confidently refactor code. Jtest also offers feedback on modified code coverage allowing teams to enforce that modified and new code has enough tests—even if the rest of the code does not.

Collaboration and Documentation

Parasoft Jtest keeps track of all test results, code coverage, and other metrics, providing living documentation for software development. Parasoft DTP analytics and reporting provides easy-to-use dashboards with high-level test status that highlights the current state of development. Test coverage and results are readily available to developers, team leads, and management.

How to Improve JUnit Test Efficiency With Parasoft Jtest

Here are some strategies developers can employ to improve JUnit test creation and execution efficiency.

Focus on Test Coverage

Test coverage is an essential aspect of unit testing. By ensuring that your tests cover a significant portion of your codebase, you increase the chances of detecting bugs and vulnerabilities.

You should define a policy about what percentage of the code should be covered with automated tests, continually measure the code coverage, and add tests as appropriate to ensure that the policy is being met. Most of the coverage will come from unit tests, but you can and should consider other kinds of tests that may more effectively and efficiently cover the code–for example, API tests or UI tests. Parasoft Jtest effectively captures and reports code coverage during runtime for all testing practices, allowing you to see code coverage from individual practices or combined together into one metric.

Use Automated + Assisted Test Creation

Parasoft Jtest provides the ability to automatically generate a suite of tests that cover multiple branches of the codebase, often achieving 60% or more code coverage with little human intervention. However, getting to higher levels of coverage often requires additional effort. To support this, Parasoft Jtest provides assisted workflows to help users build and update their unit tests more efficiently. In all, you can significantly decrease the time it takes to create unit tests—even up to 50%.

Leverage Mocking Frameworks

Parasoft Jtest integrates with mocking frameworks like Mockito, which enables the creation of test stubs or mocks. These frameworks play a complementary role to unit testing by enabling the isolation of the unit under test by replacing dependencies with controlled implementations. This way, you can concentrate on testing specific units without worrying about the behavior of external components.

Optimize Test Execution Time

As the codebase grows, test suites can become time-consuming to execute. To improve efficiency, analyze and optimize the execution time of your tests. Consider using parallel test execution, test ordering, or selective test execution based on code changes. These strategies help reduce the feedback loop and enable faster development cycles without compromising test quality. Parasoft Jtest performs test impact analysis to identify and run the tests associated with modified code, providing faster feedback for changes.

Deep Dive Into Code Coverage Problems & Solutions

Taking a deeper dive into code coverage problems and solutions, let’s examine raw coverage versus meaningful tests.

Raw Coverage vs. Meaningful Tests

If you shoot for a high-coverage number at the expense of a solid, meaningful, clean test suite, you lose value. A well-maintained suite of tests gives you confidence in your code and is even the basis for quick and safe refactoring. Noisy and/or meaningless tests mean that you can’t rely on your test suite, not for refactoring or even for release.

What happens when people measure their code coverage, especially against strict standards, is that they find out they have lower coverage than they want. And often this ends up with them chasing the coverage number, even at the expense of creating meaningful, maintainable tests.

Image of man running up a staircase made of a dollar bills leading to a large code coverage percentage sign.

This can lead to dangerous territory, where they unreasonably believe that automated JUnit testing has created meaningful tests, or they create unit tests by hand that have little meaning and are expensive to maintain.

In the real world, the ongoing costs of maintaining a test suite far outweigh the costs of creating unit tests, so it’s important to create good clean unit tests in the beginning. A sign of stable, clean tests is that you can run the tests all the time as part of your continuous integration (CI) process. If you only run the tests at release, it’s a sign that the tests are noisier than they should be. Ironically, this makes the tests even worse because they’re not being maintained.

Software testing automation is necessary with the complexity and time pressures that are common today. But the right kind of automation is necessary to create maintainable unit tests that effectively test the important logic of the application.

What Can You Do?


The first step is to measure and get a report on your current coverage, otherwise, you won’t know where you’re at and if you’re getting better. It’s important to measure all testing activities when doing this, including unit, functional, UI, and manual, and aggregate the coverage properly. This way, you’ll be putting your effort into where it has the most value—on code that isn’t tested at all—rather than code that is covered by your end-to-end testing but doesn’t happen to have a unit test. Parasoft can accurately aggregate code coverage from multiple runs and multiple types of tests to give you an accurate measure of where you’re at.


Tools that create unit test skeletons for you are a good way to start writing unit tests. Make sure those tools connect to common mocking frameworks like Mockito because real code is complicated and requires stubbing and mocking. But that’s not enough. You need to be able to:

  • Create meaningful mocks.
  • Cover all important logic in the code, including error conditions.
  • Expand simple tests with more data permutations.

Intelligent Assistance

You can do all these things manually, but it takes too much time and effort. This is an excellent place to leverage automation. For example, in addition to automatic unit test generation, Parasoft Jtest provides assisted workflows in real time in the IDE as developers work on their unit tests, integrating with open source frameworks (JUnit, Mockito) to help the user create, scale, and maintain their JUnit test suite and provide broader coverage. If you’re curious about this technology, you can learn more about why people hate unit testing and how to bring back the love.


Unit testing in Java is critical to producing high-quality software. Leveraging test automation with tools like Parasoft Jtest and testing frameworks like JUnit improves the outcomes of testing with better correctness, reliability, and security. Code coverage is often used as a key metric to measure whether enough testing is being done.

If coverage is an issue for your project, make sure you’re measuring it right and collecting data from all the tests you run. As you expand your coverage with unit tests, leverage guided test creation to quickly create and expand your tests to get meaningful, maintainable code coverage. Parasoft Jtest will create maintainable tests as your code grows and changes.

Make unit testing easier and faster with AI-enhanced Parasoft Jtest.