Project Technical Lead
Java unit tests and JUnit – tips and tricks for writing tests
Testing is a critical part of software development because it allows us to verify that different parts of our code work correctly and meet the requirements. Unit testing is one of the main types of testing, which involves testing individual pieces of code, such as methods and classes, separately from the rest of the application.
In Java, unit testing is a common practice, but writing efficient and reliable unit tests requires some knowledge and skills. In this article, we’ll take a look at some useful tips and tricks to help you write quality unit tests.
Use the JUnit library
JUnit is the most popular testing library for the Java language, providing an environment for writing and executing unit tests. It allows us to define test cases using annotations and provides a number of methods for verifying the expected results. To get started, you need to include JUnit as a dependency in your project.
Separate the tests from the main source code
You should keep the test classes separate from the main source code, to avoid the possibility of running them in a production environment. The best place for tests is the relative path src/main/test, and this is also where build tools such as Maven will look for implemented tests.
Give tests descriptive names
When writing unit tests, it is important to name test methods in a clear and concise manner. Test methods should start with the word “test” and clearly describe what the test is trying to verify. This will help to identify problems quickly if any of the tests fail.
Start with simple tests
When you start writing tests, focus on simple cases that cover the basic functionality of your classes. This will help you to ensure that the basic components of your application are working correctly, and then you can gradually expand your test scenarios.
Test boundary values
Boundary values are a common source of errors in code. When writing tests, make sure you include boundary values that can affect the behaviour of your code. These include uninitialized object values (null), negative values, maximum and minimum values, and invalid inputs. Testing for these boundary conditions can reveal potential bugs in your code.
Isolate tests from external dependencies
Unit tests should be independent and should not depend on external sources such as databases, files or web services. To achieve this, you can use mocking or stubbing to simulate the behaviour of these dependencies. This ensures that test failures are not caused by problems with external dependencies.
Use assert methods
The JUnit library provides several assert methods that allow you to verify that the expected output of your test is correct. The most commonly used are assertEquals(), assertTrue(), assertFalse(), etc. Using the correct assert methods is critical to successful test validation.
Write parameterized tests
JUnit supports parameterized tests that allow you to run the same tests with different input values. This makes it easier to test different scenarios and minimizes duplication of test code.
Run tests regularly
Don’t forget to run all your unit tests regularly. It is often the case that changes in one part of the code can affect another part of the application. By running tests regularly, you can catch problems before they reach the production environment.
Test exception handling
Incorrect exception handling can cause your program to crash. Therefore, test that your methods correctly evaluate the expected exceptions and can respond to them correctly.
In JUnit, you can use the @Test annotation along with the expected parameter to verify that the method will throw an exception. For example: @Test(expected = IllegalArgumentException.class)
Analyze code coverage
Test coverage is a metric that shows the percentage of code covered by tests. There are many tools (e.g. JaCoCo, Cobertura) that allow you to analyze code coverage by tests. These tools will show you what percentage of your code is covered by tests, allowing you to identify parts of your code that are not being tested.
Keep your tests up-to-date
When you make changes to your code, don’t forget to update the corresponding tests. Keep your test scenarios up to date and ensure that new features are properly tested.
With these tips and tricks, you should be ready to start writing effective unit tests in Java. Remember that well-written tests improve the quality of your code and can save you a lot of time later when analyzing bugs in your code.
