@ValueSource for simple values in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a parameterized test with @ValueSource

What will be the output when running this JUnit 5 parameterized test?

JUnit

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
import static org.junit.jupiter.api.Assertions.assertTrue;

class SampleTest {
    @ParameterizedTest
    @ValueSource(strings = {"apple", "banana", "cherry"})
    void testStringLength(String fruit) {
        assertTrue(fruit.length() > 3);
    }
}

A All tests pass successfully.

B Test fails for "cherry" because length is not greater than 3.

C Test fails for "banana" because length is not greater than 3.

D Test fails for "apple" because length is not greater than 3.

💡 Hint

Check the length of each string in the @ValueSource array.

Each string in the array has length greater than 3, so the assertion assertTrue(fruit.length() > 3) passes for all.

❓ assertion

intermediate

Correct assertion for integer values from @ValueSource

Given this parameterized test, which assertion correctly verifies that the input number is even?

JUnit

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
import static org.junit.jupiter.api.Assertions.*;

class NumberTest {
    @ParameterizedTest
    @ValueSource(ints = {2, 4, 6, 7})
    void testIsEven(int number) {
        // Which assertion is correct here?
    }
}

A assertFalse(number % 2 == 0);

B assertTrue(number % 2 == 0);

C assertEquals(1, number % 2);

D assertEquals(0, number / 2);

💡 Hint

Even numbers have zero remainder when divided by 2.

The assertion assertTrue(number % 2 == 0) correctly checks if the number is even.

Option B is the opposite, C checks for odd numbers, and D compares division result incorrectly.

🔧 Debug

advanced

Identify the error in this @ValueSource usage

What error will occur when running this test class?

JUnit

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

class DebugTest {
    @ParameterizedTest
    @ValueSource(strings = {"one", null, "three"})
    void testStrings(String input) {
        System.out.println(input);
    }
}

A NullPointerException at runtime.

B Test runs successfully printing all values including null.

C Compilation error due to null in @ValueSource.

D IllegalArgumentException: @ValueSource does not support null values.

💡 Hint

Check if @ValueSource allows null elements in its arrays.

@ValueSource does not support null values and throws IllegalArgumentException when null is included.

🧠 Conceptual

advanced

Behavior of @ValueSource with empty arrays

What happens when a parameterized test uses @ValueSource with an empty array?

JUnit

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

class EmptyTest {
    @ParameterizedTest
    @ValueSource(strings = {})
    void testEmpty(String input) {
        System.out.println(input);
    }
}

A Test is skipped because there are no values to run.

B Test runs once with input as null.

C Test runs zero times and passes silently.

D Test fails with IllegalArgumentException.

💡 Hint

Think about how parameterized tests behave with no parameters.

When @ValueSource provides an empty array, the test method is not executed at all, so it runs zero times and passes silently.

❓ framework

expert

Combining @ValueSource with other parameter sources

Which statement about combining @ValueSource with other parameter sources in JUnit 5 is correct?

A @ValueSource cannot be combined with other parameter sources; only one source per test method is allowed.

B Multiple @ValueSource annotations can be used on the same test method.

C @ValueSource can be combined with @CsvSource in the same @ParameterizedTest method.

D @ValueSource supports multiple types of values in one annotation (e.g., ints and strings).

💡 Hint

Check JUnit 5 rules about parameter sources per test method.

JUnit 5 allows only one parameter source annotation per @ParameterizedTest method. Combining @ValueSource with others like @CsvSource in the same method is not allowed.