Custom display names for parameters in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a parameterized test with custom display names

Consider this JUnit 5 parameterized test snippet using @ValueSource and @DisplayName. What will be the display name shown for the test case with parameter value 5?

JUnit

@ParameterizedTest(name = "Test with number={0}")
@ValueSource(ints = {3, 5, 7})
void testNumbers(int number) {
    assertTrue(number > 0);
}

A Test case 5

B Test with number=5

C testNumbers with parameter 5

D testNumbers(5)

💡 Hint

Look at the @ParameterizedTest annotation's name attribute and how {0} is replaced.

The name attribute in @ParameterizedTest uses {0} as a placeholder for the first parameter value. So for parameter 5, the display name is 'Test with number=5'.

❓ assertion

intermediate

Assertion on display name in a parameterized test

In a JUnit 5 parameterized test, which assertion correctly verifies that the display name for the parameter value "apple" is "Fruit: apple" when using @ParameterizedTest(name = "Fruit: {0}")?

A assertEquals("Fruit: apple", testInfo.getDisplayName());

B assertTrue(testInfo.getDisplayName().contains("apple"));

C assertEquals("apple", testInfo.getDisplayName());

D assertNotNull(testInfo.getDisplayName());

💡 Hint

The display name uses the name pattern with {0} replaced by the parameter.

The display name is exactly 'Fruit: apple' because the name pattern is 'Fruit: {0}' and {0} is replaced by the parameter value 'apple'.

🔧 Debug

advanced

Identify the error in custom display name usage

What error will occur when running this JUnit 5 parameterized test with the following annotation? @ParameterizedTest(name = "Value is {1}") @ValueSource(strings = {"x", "y"}) void testValues(String val) { assertNotNull(val); }

JUnit

@ParameterizedTest(name = "Value is {1}")
@ValueSource(strings = {"x", "y"})
void testValues(String val) {
    assertNotNull(val);
}

A NullPointerException during test execution

B Test runs successfully with display names 'Value is x' and 'Value is y'

C Compilation error due to invalid annotation syntax

D IndexOutOfBoundsException at runtime

💡 Hint

Check the placeholder index used in the name attribute and the number of parameters.

The placeholder {1} refers to the second parameter, but the test method has only one parameter. This causes an IndexOutOfBoundsException at runtime when JUnit tries to replace {1}.

❓ framework

advanced

Custom display names with @CsvSource in JUnit 5

Given this parameterized test using @CsvSource with custom display names, what will be the display name for the test case with parameters ("John", 25)? @ParameterizedTest(name = "User {0} is {1} years old") @CsvSource({"John, 25", "Jane, 30"}) void testUser(String name, int age) { assertTrue(age > 0); }

JUnit

@ParameterizedTest(name = "User {0} is {1} years old")
@CsvSource({"John, 25", "Jane, 30"})
void testUser(String name, int age) {
    assertTrue(age > 0);
}

A User John is 25 years old

B User {0} is {1} years old

C User 25 is John years old

D testUser(John, 25)

💡 Hint

The placeholders {0} and {1} correspond to the first and second parameters respectively.

The display name replaces {0} with 'John' and {1} with 25, resulting in 'User John is 25 years old'.

🧠 Conceptual

expert

Understanding limitations of custom display names in JUnit 5 parameterized tests

Which statement about custom display names in JUnit 5 parameterized tests is TRUE?

A Custom display names can include expressions evaluated at runtime to format parameters.

B You can use named placeholders like {name} in the name attribute to refer to parameters by name.

C The placeholders in the name attribute must be zero-based indexes like {0}, {1}, corresponding to method parameters.

D JUnit 5 automatically generates display names using parameter types if no name attribute is provided.

💡 Hint

Think about how JUnit 5 replaces placeholders in the name attribute.

JUnit 5 uses zero-based numeric placeholders like {0}, {1} to refer to parameters by position. Named placeholders or runtime expressions are not supported in the name attribute.