@CsvSource for inline CSV data in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a JUnit test using @CsvSource with multiple parameters

What is the output of the following JUnit test method when run?

Note: The test asserts that the sum of two integers equals the expected result.

JUnit

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

public class CalculatorTest {
    @ParameterizedTest
    @CsvSource({"1, 2, 3", "4, 5, 9", "3, 3, 6"})
    void testAdd(int a, int b, int expected) {
        assertEquals(expected, a + b);
    }
}

A The test fails on the third case because 3 + 3 is not 6.

B The test fails on the second case because 4 + 5 is not 9.

C All 3 test cases pass successfully.

D The test fails on all cases due to a syntax error in @CsvSource.

💡 Hint

Check the addition results for each input set.

Each pair of integers is added and compared to the expected sum. All sums match the expected values, so all tests pass.

❓ assertion

intermediate

Identify the failing assertion in a @CsvSource test

Given the following test method, which assertion will fail during execution?

JUnit

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

public class StringTest {
    @ParameterizedTest
    @CsvSource({"hello, HELLO", "world, WORLD", "java, Java"})
    void testToUpperCase(String input, String expected) {
        assertEquals(expected, input.toUpperCase());
    }
}

A The assertion for input 'world' fails.

B All assertions pass successfully.

C The assertion for input 'hello' fails.

D The assertion for input 'java' fails.

💡 Hint

Check how the expected string compares to the actual uppercase conversion.

For 'java', expected is 'Java' but input.toUpperCase() returns 'JAVA', so the assertion fails.

❓ locator

advanced

Best practice for specifying string values with commas in @CsvSource

Which option correctly specifies a string containing a comma in a @CsvSource annotation?

A @CsvSource({"'Hello, World'", "Test"})

B @CsvSource({"Hello, World", "Test"})

C @CsvSource({"""Hello, World""", "Test"})

D @CsvSource({"Hello\, World", "Test"})

💡 Hint

Look for the correct way to escape or quote commas inside CSV strings.

In @CsvSource, strings containing commas must be enclosed in single quotes to be treated as one value.

🔧 Debug

advanced

Identify the cause of a runtime error in a @CsvSource test

Why does the following test method throw an exception during execution?

JUnit

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

public class DivisionTest {
    @ParameterizedTest
    @CsvSource({"10, 2, 5", "8, 0, 0"})
    void testDivide(int numerator, int denominator, int expected) {
        assertEquals(expected, numerator / denominator);
    }
}

A The expected value in the second case is incorrect causing assertion failure.

B Division by zero occurs in the second test case causing ArithmeticException.

C The @CsvSource syntax is invalid causing a compilation error.

D The test method parameters do not match the number of CSV values.

💡 Hint

Consider what happens when denominator is zero in division.

Dividing by zero causes an ArithmeticException at runtime, which stops the test execution.

❓ framework

expert

Understanding parameter conversion in @CsvSource with custom types

Given the following test and supporting code, what will be the result of running the test?

JUnit

import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.CsvSource;
import org.junit.jupiter.params.converter.ConvertWith;
import org.junit.jupiter.params.converter.SimpleArgumentConverter;

class Color {
    String name;
    Color(String name) { this.name = name; }
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Color)) return false;
        return name.equals(((Color) o).name);
    }
}

class ColorConverter extends SimpleArgumentConverter {
    @Override
    protected Object convert(Object source, Class<?> targetType) {
        if (source instanceof String && targetType == Color.class) {
            return new Color(((String) source).toLowerCase());
        } else {
            throw new IllegalArgumentException("Conversion failed");
        }
    }
}

public class ColorTest {
    @ParameterizedTest
    @CsvSource({"RED, red", "Blue, blue", "Green, green"})
    void testColorConversion(@ConvertWith(ColorConverter.class) Color input, Color expected) {
        assertEquals(expected, input);
    }
}

A The test throws IllegalArgumentException due to failed conversion of expected parameter.

B The test fails because expected parameters are not converted and cause assertion failures.

C All test cases pass because input strings are converted to lowercase Color objects matching expected.

D The test fails compilation because @ConvertWith cannot be applied to multiple parameters.

💡 Hint

Consider how JUnit converts parameters and which parameters have converters applied.

Only the 'input' parameter is converted using ColorConverter. The 'expected' parameter remains a String, so the assertion compares Color to String causing failure or exception.