Blog

JUnit is a popular testing framework used in Java projects. It provides a way to write and execute automated tests for Java code. In JUnit, Parameterized Tests allow developers to test the same functionality with different input data sets, which can save time and improve the efficiency of testing. In this blog post, we will discuss JUnit Parameterized Tests and how they can be used to test with multiple data sets.

What are JUnit Parameterized Tests?

JUnit Parameterized Tests are a way to test the same functionality with multiple input data sets. With Parameterized Tests, developers can write a single test method that accepts input data as parameters, and JUnit will execute the test method for each data set.

Parameterized Tests are implemented using the @Parameterized annotation. The @Parameterized annotation is used to indicate that the test method should be executed multiple times with different input data. The input data is typically defined as a collection or an array, and is provided to the test method as a parameter.

Here’s an example of how to use JUnit Parameterized Tests to test a simple method that calculates the sum of two numbers:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;

import java.util.Arrays;
import java.util.Collection;

import static org.junit.Assert.assertEquals;

@RunWith(Parameterized.class)
public class MyTest {
    private int num1;
    private int num2;
    private int expected;

    public MyTest(int num1, int num2, int expected) {
        this.num1 = num1;
        this.num2 = num2;
        this.expected = expected;
    }

    @Parameterized.Parameters
    public static Collection<Object[]> data() {
        return Arrays.asList(new Object[][]{
                {1, 2, 3},
                {2, 3, 5},
                {5, 5, 10},
                {10, 0, 10},
                {-5, 5, 0}
        });
    }

    @Test
    public void testSum() {
        assertEquals(expected, sum(num1, num2));
    }

    private int sum(int num1, int num2) {
        return num1 + num2;
    }
}

In this example, we have a test class named MyTest, which has a single test method named testSum(). The test method accepts two integers (num1 and num2) and an expected result (expected) as parameters, and calculates the sum of num1 and num2 using the sum() method.

The @Parameterized annotation is used to indicate that the test method should be executed multiple times with different input data. The input data is defined in the data() method, which returns a collection of arrays. Each array represents a set of input data, and contains the values of num1, num2, and expected.

The test method is executed for each set of input data, and the expected result is compared to the actual result using the assertEquals() method.

More details on parameterized tests:

1. Data Sources: The input data for Parameterized Tests can come from a variety of sources, including arrays, collections, or external files. The @Parameterized annotation supports multiple data sources, and can be used to read data from CSV, XML, or JSON files.
2. Dynamic Test Generation: In addition to running tests with pre-defined data sets, JUnit also supports dynamic test generation. With dynamic test generation, developers can generate input data programmatically and pass it to the test method.
3. Test Naming: JUnit Parameterized Tests generate multiple test instances, each with its own set of input data. By default, JUnit uses the name of the test method to generate the names of the individual tests. However, developers can customize the test names by implementing the org.junit.runner.Describable interface and overriding the describeChild() method.
4. Test Failures: When a Parameterized Test fails, JUnit provides detailed information about the failing test instance, including the input data that caused the failure. This makes it easier for developers to diagnose and fix errors in their code.
5. Test Suites: JUnit Parameterized Tests can be included in test suites, along with other types of tests. Test suites provide a way to organize and run multiple tests together, and can be executed with a single command.

Differences in Parameterized Tests between JUnit 4 and JUnit 5

1. Annotation: In JUnit 4, the @RunWith annotation was used to run Parameterized Tests. In JUnit 5, the @ParameterizedTest annotation is used instead.
2. Parameter Source: JUnit 5 introduces a new parameter source model, which allows developers to specify different sources of input data for Parameterized Tests. In addition to arrays and collections, JUnit 5 supports parameter sources such as CSV files, Value Sources, and Enum Sources.
3. Test Instance: In JUnit 4, a new test instance was created for each set of input data. In JUnit 5, the same test instance is reused for all sets of input data, which can improve performance and reduce memory usage.
4. Test Name: In JUnit 4, the test name was generated automatically based on the test method name and the input data. In JUnit 5, developers can customize the test name using the @DisplayName annotation.

New Features in JUnit 5 Parameterized Tests

1. Parameter Resolver: JUnit 5 introduces the concept of a Parameter Resolver, which allows developers to inject additional parameters into test methods. Parameter Resolvers can be used to inject dependencies or other context objects into test methods.
2. Dynamic Test Generation: JUnit 5 supports dynamic test generation, which allows developers to generate input data and test cases programmatically. Dynamic test generation can be used to create tests with complex input data sets, or to generate tests at runtime based on external factors.
3. Repeated Tests: JUnit 5 introduces the @RepeatedTest annotation, which allows developers to repeat a test method a specified number of times with different input data. Repeated Tests can be used to test the behavior of a system over multiple iterations or to simulate load testing.
4. Test Execution Order: JUnit 5 allows developers to specify the order in which Parameterized Tests are executed using the @TestMethodOrder annotation. This can be used to ensure that tests are executed in a specific order, or to group tests by functionality or priority.

Conclusion

JUnit Parameterized Tests provide a way to test the same functionality with multiple input data sets. Parameterized Tests can save time and improve the efficiency of testing, as developers can test a wide range of input data with a single test method. By using the @Parameterized annotation and providing the input data as a collection or an array, developers can easily create Parameterized Tests in JUnit.