@CsvFileSource for external CSV in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of JUnit test using @CsvFileSource with external CSV

Consider this JUnit 5 test method that uses @CsvFileSource to read data from an external CSV file named data.csv located in src/test/resources. What will be the output when the test runs?

JUnit

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

public class CalculatorTest {

    @ParameterizedTest
    @CsvFileSource(resources = "/data.csv", numLinesToSkip = 1)
    void testAdd(int a, int b, int expectedSum) {
        assertEquals(expectedSum, a + b);
    }
}

A The test passes for all rows in data.csv except the header line.

B The test fails because the CSV file path is incorrect.

C The test throws a runtime exception due to missing default constructor.

D The test is ignored because @CsvFileSource requires inline CSV data.

💡 Hint

Check how @CsvFileSource loads files from the resources folder and the effect of numLinesToSkip.

The @CsvFileSource annotation loads the CSV file from the classpath resource path. The numLinesToSkip=1 skips the header line. The test method receives each row's values as parameters and asserts the sum. Since the file is correctly located and formatted, the test passes for all data rows.

❓ assertion

intermediate

Correct assertion for @CsvFileSource test with string inputs

Given this parameterized test using @CsvFileSource with string inputs from an external CSV, which assertion correctly verifies that the input string is not empty?

JUnit

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

public class StringTest {

    @ParameterizedTest
    @CsvFileSource(resources = "/strings.csv")
    void testNotEmpty(String input) {
        // Which assertion is correct here?
    }
}

A assertFalse(input.isEmpty());

B assertTrue(input == null);

C assertEquals(input.length(), 0);

D assertNull(input);

💡 Hint

Think about how to check that a string is not empty.

assertFalse(input.isEmpty()) checks that the string is not empty. The other options either check for null or empty incorrectly.

❓ locator

advanced

Correct resource path for @CsvFileSource external CSV file

You want to load a CSV file named test-data.csv located in src/test/resources/data/ folder using @CsvFileSource. Which resource path is correct?

A "src/test/resources/data/test-data.csv"

B "data/test-data.csv"

C "/data/test-data.csv"

D "/src/test/resources/data/test-data.csv"

💡 Hint

Remember that resource paths are relative to the classpath root and start with a slash.

The resource path in @CsvFileSource must start with a slash and be relative to the classpath root. So "/data/test-data.csv" is correct. The full file system path or missing slash are incorrect.

🔧 Debug

advanced

Identify the cause of failure in @CsvFileSource test

This test fails with java.lang.IllegalArgumentException: CSV file not found. What is the most likely cause?

JUnit

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

public class DebugTest {

    @ParameterizedTest
    @CsvFileSource(resources = "/testdata.csv")
    void testData(int x, int y) {
        // test logic
    }
}

A The test method parameters do not match the CSV columns.

B The CSV file is not located in the classpath root or resources folder.

C The CSV file has a header but numLinesToSkip is not set.

D The test method is missing the @Test annotation.

💡 Hint

Check the file location and classpath setup.

The error indicates the file cannot be found in the classpath. The most common cause is that the CSV file is not placed in the src/test/resources folder or the path is incorrect.

❓ framework

expert

Behavior of @CsvFileSource with empty lines in external CSV

When using @CsvFileSource with an external CSV file that contains empty lines, what happens during test execution?

A JUnit fails to start tests and reports a syntax error in the CSV.

B JUnit skips empty lines automatically and runs tests only on valid rows.

C JUnit treats empty lines as rows with empty strings and passes empty parameters.

D JUnit throws a <code>ParameterResolutionException</code> due to missing parameters.

💡 Hint

Consider how JUnit handles parameterized tests when parameters are missing.

Empty lines in the CSV cause JUnit to receive no parameters for that test invocation, leading to a ParameterResolutionException because the test method expects parameters.