How to Use @ParameterizedTest in JUnit for Data-Driven Testing

Use @ParameterizedTest in JUnit to run the same test method multiple times with different inputs. Combine it with annotations like @ValueSource or @CsvSource to provide test data. This helps test various cases without writing separate test methods.

Syntax

The @ParameterizedTest annotation marks a test method to run multiple times with different parameters. You provide the parameters using source annotations like @ValueSource, @CsvSource, or others. The test method must accept parameters matching the data types provided.

• @ParameterizedTest: Marks the method as parameterized.
• @ValueSource: Supplies a single array of literals (ints, strings, etc.).
• @CsvSource: Supplies multiple comma-separated values per test run.
• Method parameters receive the data for each run.

java

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

class ExampleTest {
    @ParameterizedTest
    @ValueSource(strings = {"apple", "banana", "cherry"})
    void testWithStrings(String fruit) {
        System.out.println(fruit);
    }
}

Example

This example shows a parameterized test that checks if a number is even. It uses @ValueSource to provide multiple integers. The test runs once per number and asserts the number is even.

java

import static org.junit.jupiter.api.Assertions.assertTrue;

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

class NumberTest {
    @ParameterizedTest
    @ValueSource(ints = {2, 4, 6, 8, 10})
    void testIsEven(int number) {
        assertTrue(number % 2 == 0, number + " should be even");
    }
}

Output

Test passed 5 times with inputs: 2, 4, 6, 8, 10

Common Pitfalls

• Forgetting to add a source annotation like @ValueSource causes the test not to run.
• Method parameters must match the data types provided by the source exactly.
• Using unsupported types in @ValueSource leads to errors; use @CsvSource or custom providers instead.
• Mixing @Test and @ParameterizedTest on the same method is invalid.

java

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

class WrongTest {
    // Wrong: No source annotation
    @ParameterizedTest
    void testWithoutSource(String input) {
        // This will fail to run
    }

    // Correct:
    @ParameterizedTest
    @ValueSource(strings = {"a", "b"})
    void testWithSource(String input) {
        // Runs correctly
    }
}

Quick Reference

Annotation	Purpose	Example Usage
@ParameterizedTest	Marks a test method to run with multiple inputs	@ParameterizedTest
@ValueSource	Provides a single array of literals	@ValueSource(strings = {"a", "b"})
@CsvSource	Provides multiple comma-separated values per run	@CsvSource({"1, 'one'", "2, 'two'"})
@MethodSource	Uses a method to supply arguments	@MethodSource("methodName")

Key Takeaways

Use @ParameterizedTest to run tests multiple times with different inputs.

Provide test data with source annotations like @ValueSource or @CsvSource.

Ensure method parameters match the types of provided data exactly.

Never forget to add a source annotation or the test won't run.

Use parameterized tests to reduce code duplication and improve coverage.