Multiple parameter types in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of JUnit test with multiple parameter types

Consider the following JUnit 5 parameterized test method using @CsvSource with mixed parameter types. What will be the test execution result for the given inputs?

JUnit

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

class CalculatorTest {
    @ParameterizedTest
    @CsvSource({
        "2, 3, 5",
        "-1, 1, 0",
        "0, 0, 0",
        "5, -3, 2"
    })
    void testAdd(int a, int b, int expected) {
        assertEquals(expected, a + b);
    }
}

A The test with inputs (0, 0, 0) throws a runtime exception.

B The test with inputs (5, -3, 2) fails due to wrong expected value.

C The test with inputs (-1, 1, 0) fails due to type mismatch error.

D All 4 tests pass successfully.

💡 Hint

Check the addition results for each input set carefully.

Each test case adds the two integers and compares to the expected sum. All expected values match the actual sums, so all tests pass.

❓ assertion

intermediate

Correct assertion for mixed parameter types in JUnit

You have a parameterized test method with parameters: String name, int age, boolean active. Which assertion correctly verifies that age is greater than 18 and active is true?

JUnit

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

void testUser(String name, int age, boolean active) {
    // Which assertion is correct?
}

A assertFalse(age <= 18 || !active);

B assertEquals(true, age > 18 && active);

C assertTrue(age > 18 && active);

D assertTrue(age > 18 || active);

💡 Hint

Use assertTrue with the exact condition you want to verify.

Option C directly asserts that age is greater than 18 and active is true. Option C works but is less clear. Option C asserts the negation, which is correct logically but less direct. Option C uses OR instead of AND, so it allows incorrect cases.

🔧 Debug

advanced

Identify the cause of failure in mixed parameter JUnit test

Given this parameterized test using @MethodSource, why does the test fail with a ParameterResolutionException?

JUnit

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.MethodSource;
import java.util.stream.Stream;

class UserTest {
    static Stream<Object[]> userProvider() {
        return Stream.of(
            new Object[]{"Alice", 30, true},
            new Object[]{"Bob", "twenty", false}
        );
    }

    @ParameterizedTest
    @MethodSource("userProvider")
    void testUser(String name, int age, boolean active) {
        // test logic
    }
}

A The second parameter '"twenty"' cannot be converted to int, causing the failure.

B The method userProvider() is not static, causing the failure.

C The test method parameters do not match the provider method return type.

D The boolean parameter 'active' is not boxed, causing the failure.

💡 Hint

Check the types of values provided for each parameter.

The second test case provides a String "twenty" where an int is expected, causing a ParameterResolutionException during test execution.

❓ framework

advanced

JUnit 5 parameterized test with multiple parameter types and custom converter

Which JUnit 5 feature allows you to convert a String parameter to a custom object type in a parameterized test?

A @ConvertWith annotation with a custom ArgumentConverter implementation

B @CsvSource with inline lambda conversion

C @ValueSource with a custom parser method

D @MethodSource with automatic type inference

💡 Hint

Look for annotations that handle parameter conversion explicitly.

JUnit 5 provides @ConvertWith to specify a custom ArgumentConverter class to convert String inputs to custom types in parameterized tests.

🧠 Conceptual

expert

Handling multiple parameter types in JUnit parameterized tests with null values

In a JUnit 5 parameterized test with parameters (String name, Integer age, Boolean active), which approach correctly allows passing null values for age and active using @CsvSource?

A Use empty strings for nulls and annotate the test method with @NullAndEmptySource

B Use the string 'null' in @CsvSource and annotate parameters with @ConvertWith(NullConverter.class)

C Use the string 'null' in @CsvSource and annotate the test method with @NullSource

D Use the string 'null' in @CsvSource and annotate parameters with @NullAndEmptySource

💡 Hint

Consider how JUnit converts string literals to null for non-String parameters.

JUnit 5 does not automatically convert the string 'null' to null for non-String parameters. Using a custom converter with @ConvertWith allows interpreting 'null' as null values.