How to pass a null value in JUnit 5 parameterized tests

By mkyong | Updated: January 28, 2022

Viewed: 22,872 (+256 pv/w)

Tags: junit 5 parameter test unit test

How to pass a null for the below parameterized tests?

@ParameterizedTest(name = "#{index} - Run test with args={0}")
@ValueSource(strings = {"", " "})
// @ValueSource(strings = {"", " ", null}) // compile error
void testBlankIncludeNull(String input) {
	 assertTrue(StringUtils.isBlank(input));
}

1. Solution – @NullSource

Since JUnit 5.4 and above, we can use the @NullSource to pass a null value to the parameterized tests.

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

	@ParameterizedTest(name = "#{index} - Run test with args={0}")
	@NullSource	// pass a null value
	@ValueSource(strings = {"", " "})
	void testBlankIncludeNull(String input) {
	    assertTrue(StringUtils.isBlank(input));
	}

2. Solution – @MethodSource

Alternatively, we can use @MethodSource to provide arguments (including null value) for the tests.

@ParameterizedTest(name = "#{index} - Run test with args={0}")
@MethodSource("blankOrNullStrings")
void testBlankIncludeNull(String input) {
		assertTrue(StringUtils.isBlank(input));
}

static Stream<String> blankOrNullStrings() {
		return Stream.of("", " ", null);
}

3. Download Source Code

4. References

• @NullSource JavaDoc
• Introduce @NullSource parameterized tests
• JUnit 5 Parameterized Tests – User Guide
• JUnit 5 Parameterized Tests – Examples