@NullSource and @EmptySource in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the @NullSource annotation do in JUnit?

It provides a single null argument to a parameterized test method, allowing you to test how your code handles null inputs.

beginner

What is the purpose of the @EmptySource annotation in JUnit?

It supplies an empty value (like an empty string, empty collection, or empty array) as an argument to a parameterized test method to test how code behaves with empty inputs.

intermediate

Can @NullSource and @EmptySource be used together in a single test method?

Yes, you can combine @NullSource and @EmptySource to run a parameterized test with both null and empty values as inputs, helping to cover edge cases.

beginner

Example usage: How do you write a JUnit test method that tests a String parameter with null and empty values?

Use @ParameterizedTest with @NullSource and @EmptySource annotations above the test method. For example:<br>

@ParameterizedTest
@NullSource
@EmptySource
void testWithNullAndEmpty(String input) {
  // test logic here
}

beginner

Why is it important to test with @NullSource and @EmptySource?

Because null and empty inputs are common edge cases that can cause bugs if not handled properly. Testing these helps ensure your code is robust and error-free.

What input does @NullSource provide to a parameterized test?

A A zero integer

B An empty string

C A null value

D A random value

@NullSource provides a null value as input to test how the method handles null.

Which annotation supplies an empty collection or empty string to a test method?

A @NullSource

B @ValueSource

C @CsvSource

D @EmptySource

@EmptySource provides empty values like empty strings or collections to test empty input handling.

Can @NullSource be used without @ParameterizedTest?

A No, it must be used with @ParameterizedTest

B Only with @RepeatedTest

C Only with @Test

D Yes, always

@NullSource works only with @ParameterizedTest to supply null arguments.

What happens if you combine @NullSource and @EmptySource on a test method?

A The test runs only once with null

B The test runs twice: once with null, once with empty value

C The test runs only once with empty value

D The test fails to run

Combining both runs the test twice, once for each input, covering both edge cases.

Which of these is NOT a typical use of @EmptySource?

A Testing null values

B Testing empty strings

C Testing empty lists

D Testing empty arrays

@EmptySource does not provide null values; @NullSource is used for null.

Explain how @NullSource and @EmptySource help improve test coverage in JUnit parameterized tests.

Think about why testing null and empty inputs is important.

Describe how to write a JUnit test method that uses both @NullSource and @EmptySource annotations.

Remember the syntax and purpose of these annotations.