@ParameterizedTest annotation in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple @ParameterizedTest with @ValueSource

What will be the output when running this JUnit test class?

JUnit

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

public 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 "apple" because length is not greater than 3.

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

D Test fails for "cherry" 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 @ParameterizedTest with @CsvSource

Given this parameterized test, which assertion correctly verifies that the sum of two integers equals the expected result?

JUnit

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

public class MathTest {
    @ParameterizedTest
    @CsvSource({"1, 2, 3", "4, 5, 9", "10, 20, 30"})
    void testSum(int a, int b, int expected) {
        // Which assertion is correct here?
    }
}

A assertEquals(a + b, expected);

B assertTrue(a + b == expected);

C assertFalse(a + b != expected);

D assertEquals(expected, a + b);

💡 Hint

Remember the order of parameters in assertEquals(expected, actual).

The correct order for assertEquals is assertEquals(expected, actual). Option D uses this order correctly.

🔧 Debug

advanced

Identify the error in this @ParameterizedTest using @MethodSource

What error will occur when running this test class?

JUnit

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.MethodSource;
import static org.junit.jupiter.api.Assertions.assertTrue;
import java.util.stream.Stream;

public class DebugTest {
    @ParameterizedTest
    @MethodSource("stringProvider")
    void testStrings(String input) {
        assertTrue(input.length() > 0);
    }

    static Stream<String> stringProvider() {
        return Stream.of("");
    }
}

A Compilation error due to missing import for Stream.

B Test passes because empty string length is considered greater than 0.

C Test fails because input string is empty and assertion fails.

D Runtime error due to null pointer exception.

💡 Hint

Check the assertion condition and the provided input values.

The input string is empty (length 0), so assertTrue(input.length() > 0) fails causing the test to fail.

🧠 Conceptual

advanced

Understanding @ParameterizedTest with multiple parameters

Which statement about @ParameterizedTest with @CsvSource is TRUE?

A Each line in @CsvSource provides values for all parameters of the test method.

B @CsvSource can only provide one parameter per test run.

C @ParameterizedTest cannot be used with @CsvSource.

D @CsvSource automatically converts all parameters to strings only.

💡 Hint

Think about how multiple values are passed to the test method.

Each line in @CsvSource provides a comma-separated list of values that map to the test method parameters in order.

❓ framework

expert

Behavior of @ParameterizedTest with @EnumSource and filtering

Consider this test using @EnumSource with a filter. Which enum constants will the test run with?

JUnit

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.EnumSource;
import static org.junit.jupiter.api.Assertions.assertNotNull;

public class EnumTest {
    enum Color { RED, GREEN, BLUE, YELLOW }

    @ParameterizedTest
    @EnumSource(value = Color.class, names = {"RED", "BLUE"}, mode = EnumSource.Mode.EXCLUDE)
    void testColors(Color color) {
        assertNotNull(color);
    }
}

A The test does not run with any colors.

B The test runs with GREEN and YELLOW only.

C The test runs with all four colors.

D The test runs with RED and BLUE only.

💡 Hint

Check the meaning of mode = EXCLUDE with names specified.

Using mode = EXCLUDE excludes RED and BLUE, so the test runs only with GREEN and YELLOW.