@CsvFileSource for external CSV in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to load CSV data from an external file using @CsvFileSource.

JUnit

@ParameterizedTest
@CsvFileSource(resources = [1])
void testWithCsvFileSource(String input, int expected) {
    assertNotNull(input);
    assertTrue(expected >= 0);
}

Drag options to blanks, or click blank then click option'

A"data/test-data.csv"

B"/data/test-data.csv"

C"/test-data.csv"

D"test-data.csv"

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the leading slash in the resource path.

Using an incorrect file path that does not exist.

The resource path must start with a slash to load the CSV file from the classpath root.

2fill in blank

medium

Complete the code to skip the first line (header) of the CSV file in @CsvFileSource.

JUnit

@ParameterizedTest
@CsvFileSource(resources = "/data/test-data.csv", [1] = 1)
void testSkipHeader(String input, int expected) {
    assertNotNull(input);
    assertTrue(expected >= 0);
}

Drag options to blanks, or click blank then click option'

AnumLinesToSkip

BskipLines

CskipHeader

DlinesToSkip

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect attribute names like skipLines or skipHeader.

Not skipping the header line causing test failures.

The correct attribute to skip lines in @CsvFileSource is numLinesToSkip.

3fill in blank

hard

Fix the error in the @CsvFileSource annotation to correctly specify the file path.

JUnit

@ParameterizedTest
@CsvFileSource(resources = [1])
void testFilePath(String input) {
    assertNotNull(input);
}

Drag options to blanks, or click blank then click option'

A"/data/test.csv"

B"data/test.csv"

C"./data/test.csv"

D"data\\test.csv"

Attempts:

3 left

💡 Hint

Common Mistakes

Using relative paths without leading slash.

Using backslashes which are invalid in resource paths.

The resource path must start with a slash and use forward slashes for classpath resources.

4fill in blank

hard

Fill both blanks to correctly configure @CsvFileSource to skip the header and use a UTF-8 encoding.

JUnit

@ParameterizedTest
@CsvFileSource(resources = "/data/test-data.csv", [1] = 1, [2] = "UTF-8")
void testWithEncoding(String input, int expected) {
    assertNotNull(input);
    assertTrue(expected >= 0);
}

Drag options to blanks, or click blank then click option'

AnumLinesToSkip

Bencoding

Ccharset

DskipLines

Attempts:

3 left

💡 Hint

Common Mistakes

Using charset instead of encoding.

Using skipLines which is not a valid attribute.

Use numLinesToSkip to skip header lines and encoding to specify file encoding in @CsvFileSource.

5fill in blank

hard

Fill all three blanks to create a @CsvFileSource that loads a CSV file, skips the first line, and uses UTF-8 encoding.

JUnit

@ParameterizedTest
@CsvFileSource(resources = [1], [2] = 1, [3] = "UTF-8")
void testFullConfig(String input, int expected) {
    assertNotNull(input);
    assertTrue(expected >= 0);
}

Drag options to blanks, or click blank then click option'

A"/data/test.csv"

BnumLinesToSkip

Cencoding

D"data/test.csv"

Attempts:

3 left

💡 Hint

Common Mistakes

Using relative path without slash.

Wrong attribute names for skipping lines or encoding.

The resource path must start with a slash, numLinesToSkip skips the header, and encoding sets UTF-8.

Practice

1. What is the main purpose of using @CsvFileSource in JUnit tests?

easy

A. To run the same test multiple times with different data from a CSV file

B. To write data into a CSV file during test execution

C. To generate random test data automatically

D. To skip tests based on CSV file content

Solution

1. Step 1: Understand the role of @CsvFileSource

   @CsvFileSource provides external CSV data to parameterized tests, allowing multiple runs with different inputs.

2. Step 2: Compare options with this role

   Only To run the same test multiple times with different data from a CSV file correctly describes running tests multiple times with CSV data. Others describe unrelated actions.

3. Final Answer:

   To run the same test multiple times with different data from a CSV file -> Option A

4. Quick Check:

   @CsvFileSource runs tests with CSV data = B [OK]

Hint: Remember: @CsvFileSource feeds test data, not writes or skips [OK]

Common Mistakes:

• Thinking @CsvFileSource writes data instead of reading
• Confusing it with random data generation
• Assuming it controls test skipping

2. Which of the following is the correct syntax to skip the header line in a CSV file when using @CsvFileSource?

easy

A. @CsvFileSource(resources = "/data.csv", skipLines = 1)

B. @CsvFileSource(resources = "/data.csv", skipHeader = true)

C. @CsvFileSource(resources = "/data.csv", ignoreFirstLine = true)

D. @CsvFileSource(resources = "/data.csv", numLinesToSkip = 1)

Solution

1. Step 1: Recall the correct attribute for skipping lines

   The correct attribute to skip lines in @CsvFileSource is numLinesToSkip.

2. Step 2: Match options with correct attribute

   Only @CsvFileSource(resources = "/data.csv", numLinesToSkip = 1) uses numLinesToSkip = 1 which skips the first line (header).

3. Final Answer:

   @CsvFileSource(resources = "/data.csv", numLinesToSkip = 1) -> Option D

4. Quick Check:

   Skip header line = numLinesToSkip = 1 [OK]

Hint: Use numLinesToSkip to skip headers, not skipHeader or ignoreFirstLine [OK]

Common Mistakes:

• Using non-existent attributes like skipHeader or ignoreFirstLine
• Confusing skipLines with numLinesToSkip
• Forgetting to skip header causing test failures

3. Given the CSV file data.csv with content:

name,age
Alice,30
Bob,25

and the test method:

@ParameterizedTest
@CsvFileSource(resources = "/data.csv", numLinesToSkip = 1)
void testUser(String name, int age) {
    System.out.println(name + "-" + age);
}

What will be the printed output when the test runs?

medium

A. name-age
Alice-30
Bob-25

B. Alice-30
Bob-25

C. Alice-30

D. Test fails due to header line

Solution

1. Step 1: Understand numLinesToSkip effect

   numLinesToSkip=1 skips the header line "name,age" so only data lines remain.

2. Step 2: Identify printed lines

   Test runs twice, printing "Alice-30" and "Bob-25" each on separate lines.

3. Final Answer:

   Alice-30 Bob-25 -> Option B

4. Quick Check:

   Header skipped, prints data lines only = D [OK]

Hint: Skip header to avoid printing it as data [OK]

Common Mistakes:

• Not skipping header causing it to print as data
• Expecting header line to print
• Confusing output format with CSV file content

4. Consider this test snippet:

@ParameterizedTest
@CsvFileSource(resources = "/users.csv")
void testUser(String name, int age) {
    assertTrue(age > 0);
}

The CSV file users.csv has a header line. What is the likely problem when running this test?

medium

A. Test will fail because header line is treated as data causing NumberFormatException

B. Test will pass because header is ignored automatically

C. Test will fail due to missing @Test annotation

D. Test will skip all lines and run zero times

Solution

1. Step 1: Check if header is skipped

   No numLinesToSkip is set, so header line is treated as data.

2. Step 2: Understand impact on parsing

   Trying to convert header "age" to int causes NumberFormatException, failing the test.

3. Final Answer:

   Test will fail because header line is treated as data causing NumberFormatException -> Option A

4. Quick Check:

   Header not skipped causes parse error = A [OK]

Hint: Always skip header lines to avoid parsing errors [OK]

Common Mistakes:

• Assuming header is skipped automatically
• Forgetting to add numLinesToSkip=1
• Confusing @ParameterizedTest with @Test

5. You want to test a method that calculates discounts using data from a CSV file with columns: product,price,discountRate. The CSV has a header line. Which is the best way to write the parameterized test method signature and annotation to correctly read and use this data?

hard

A. @ParameterizedTest
@CsvFileSource(resources = "/discounts.csv", numLinesToSkip = 1)
void testDiscount(String product, String price, String discountRate) { ... }

B. @ParameterizedTest
@CsvFileSource(resources = "/discounts.csv")
void testDiscount(String product, int price, int discountRate) { ... }

C. @ParameterizedTest
@CsvFileSource(resources = "/discounts.csv", numLinesToSkip = 1)
void testDiscount(String product, double price, double discountRate) { ... }

D. @ParameterizedTest
@CsvFileSource(resources = "/discounts.csv", skipHeader = true)
void testDiscount(String product, double price, double discountRate) { ... }

Solution

1. Step 1: Identify header skipping attribute

   Use numLinesToSkip = 1 to skip the CSV header line.

2. Step 2: Match method parameters to CSV columns and types

   Product is String, price and discountRate are decimal numbers, so use double for price and discountRate.

3. Step 3: Check options for correctness

   @ParameterizedTest @CsvFileSource(resources = "/discounts.csv", numLinesToSkip = 1) void testDiscount(String product, double price, double discountRate) { ... } correctly uses numLinesToSkip=1 and matching parameter types. @ParameterizedTest @CsvFileSource(resources = "/discounts.csv") void testDiscount(String product, int price, int discountRate) { ... } misses skipping header and uses int instead of double. @ParameterizedTest @CsvFileSource(resources = "/discounts.csv", numLinesToSkip = 1) void testDiscount(String product, String price, String discountRate) { ... } uses String for numeric fields. @ParameterizedTest @CsvFileSource(resources = "/discounts.csv", skipHeader = true) void testDiscount(String product, double price, double discountRate) { ... } uses invalid attribute skipHeader.

4. Final Answer:

   @ParameterizedTest @CsvFileSource(resources = "/discounts.csv", numLinesToSkip = 1) void testDiscount(String product, double price, double discountRate) { ... } -> Option C

5. Quick Check:

   Skip header with numLinesToSkip=1 and match types = C [OK]

Hint: Use numLinesToSkip=1 and match parameter types to CSV columns [OK]

Common Mistakes:

• Using skipHeader instead of numLinesToSkip
• Not skipping header causing parse errors
• Mismatching parameter types with CSV data