JUnit Parameterized Tests: Revolutionizing Code Flexibility

Writing tests for different input values often requires duplicating test methods with varying parameters—an approach that often leads to code duplication and makes tests harder to maintain and more prone to errors. JUnit 5 parameterized tests enable developers to avoid this problem by executing one single test method with diverse parameters. Therefore, we can use JUnit 5 parameterized tests to:

• Simplify test case writing for every possible input
• Reduce code duplication
• Maximize code coverage for all possible scenarios
• Execute tests before deploying builds on the test environment
• Minimize execution time

First of all, in order to use parameterized tests, you have to include the junit-jupiter-params dependency.

Custom aggregators:

This functionality allows you to create parameters dynamically or apply custom logic to change the existing values. JUnit 5 allows you to achieve this by implementing a customized ArgumentsAggregator.

class CustomArgumentsAggregator implements ArgumentsAggregator {

    @Override

    public Object aggregateArguments(ArgumentsAccessor accessor, ParameterContext context) {

        return new CustomObject(accessor.getString(0), accessor.getInt(1));

    }

}

@ParameterizedTest

@ArgumentsSource(CustomArgumentsProvider.class)

void testWithCustomAggregator(CustomObject customObject) {

    // Test logic using the custom object

}

Display names

In order to create more legible names for the tests, you can use @DisplayName.. This feature is particularly useful for failed tests, allowing you to read what is going on and what is wrong easily.

Value sources

In JUnit 5, “values sources” is a feature that allows you to provide specific datasets as arguments to the parameters of a parameterized test method. This is useful when you want to run the same test with different datasets.

Instead of manually providing a list of values for the parameters of a parameterized test method, you can use predefined value sources, such as @ValueSource, to specify datasets more conveniently. Other types of sources include @EnumSource, @MethodSource, and @CsvSource.

However, you should take into account that the value sources feature only supports these types:

• short (with the shorts attribute)
• byte (bytes attribute)
• char (chars attribute)
• java.lang.String (strings attribute)
• java.lang.Class (classes attribute)
• int (ints attribute)
• float (floats attribute)
• long (longs attribute)
• double (doubles attribute)

Null and empty values

When performing tests, it’s important to validate if the application is going to work correctly when handling null and/or empty values. In order to perform these tests, we can pass a null and empty value using annotations.

Parameterized testing in JUnit 5 is an indispensable tool in the arsenal of any developer committed to software quality. This revolutionary approach saves valuable time by enabling the testing of code with a variety of data without the need to replicate test methods for each scenario. The flexibility and adaptability offered by parameterized testing not only simplify test writing but also improve the maintainability of test code by reducing duplication and unnecessary complexity.

If you are a developer looking to boost your efficiency and explore a wide range of situations and conditions in a single test, parameterized tests in JUnit 5 might be one of your best allies in the landscape of software testing.