@NullAndEmptySource in JUnit - Test Execution Trace

Test Overview

This test uses the @NullAndEmptySource annotation in JUnit to run the same test method twice: once with a null input and once with an empty string. It verifies that the method handles both cases correctly by returning false.

Test Code - JUnit 5

JUnit

import static org.junit.jupiter.api.Assertions.assertFalse;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.NullAndEmptySource;

public class InputValidatorTest {

    @ParameterizedTest
    @NullAndEmptySource
    void testIsValidInputWithNullAndEmpty(String input) {
        InputValidator validator = new InputValidator();
        boolean result = validator.isValidInput(input);
        assertFalse(result, "Input should be invalid for null or empty string");
    }
}

class InputValidator {
    public boolean isValidInput(String input) {
        return input != null && !input.isEmpty();
    }
}

Execution Trace - 4 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initializes the test class InputValidatorTest	—	PASS
2	Runs parameterized test with input = null	InputValidator instance created; input parameter is null	assertFalse(result) where result = isValidInput(null)	PASS
3	Runs parameterized test with input = "" (empty string)	InputValidator instance created; input parameter is empty string	assertFalse(result) where result = isValidInput("")	PASS
4	Test ends	All parameterized test cases executed	—	PASS

Failure Scenario

Failing Condition: The isValidInput method returns true for null or empty string inputs

Execution Trace Quiz - 3 Questions

What inputs does the @NullAndEmptySource annotation provide to the test method?

A null and empty string

B null and whitespace string

C empty string and whitespace string

D null only

Key Result

Using @NullAndEmptySource in JUnit parameterized tests helps verify that methods correctly handle null and empty inputs, which are common edge cases that can cause bugs if not tested.

Practice

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

easy

A. To run tests only when inputs are non-null and non-empty

B. To skip tests that have null or empty inputs

C. To automatically provide null and empty values as test inputs

D. To generate random test data for parameterized tests

Solution

1. Step 1: Understand the role of @NullAndEmptySource

   @NullAndEmptySource is used to add null and empty values automatically to parameterized tests.

2. Step 2: Identify its purpose in testing

   This helps test how the code behaves with missing or empty inputs without manually adding those cases.

3. Final Answer:

   To automatically provide null and empty values as test inputs -> Option C

4. Quick Check:

   @NullAndEmptySource adds null and empty inputs [OK]

Hint: Remember: @NullAndEmptySource adds null and empty inputs [OK]

Common Mistakes:

• Thinking it skips tests with null or empty inputs
• Confusing it with random data generators
• Assuming it filters out null or empty values

2. Which of the following is the correct way to use @NullAndEmptySource in a JUnit 5 parameterized test method?

easy

A. @Test
@NullAndEmptySource
void testMethod(String input) { ... }

B. @Test
@NullAndEmptySource
void testMethod() { ... }

C. @ParameterizedTest
@NullAndEmptySource
void testMethod() { ... }

D. @ParameterizedTest
@NullAndEmptySource
void testMethod(String input) { ... }

Solution

1. Step 1: Check annotation compatibility

   @NullAndEmptySource must be used with @ParameterizedTest to supply parameters.

2. Step 2: Verify method signature

   The test method must accept a parameter to receive the null or empty value.

3. Final Answer:

   @ParameterizedTest @NullAndEmptySource void testMethod(String input) { ... } -> Option D

4. Quick Check:

   @NullAndEmptySource needs @ParameterizedTest and parameter [OK]

Hint: Use @NullAndEmptySource only with @ParameterizedTest and parameters [OK]

Common Mistakes:

• Using @NullAndEmptySource with @Test instead of @ParameterizedTest
• Writing test methods without parameters
• Forgetting to annotate with @ParameterizedTest

3. Given the following test code, what will be the total number of test invocations executed?

@ParameterizedTest
@NullAndEmptySource
@ValueSource(strings = {"hello", "world"})
void testStrings(String input) {
    // test logic here
}

medium

A. 4

B. 3

C. 2

D. 5

Solution

1. Step 1: Count inputs from @NullAndEmptySource

   @NullAndEmptySource adds two inputs: null and empty string ("").

2. Step 2: Count inputs from @ValueSource

   @ValueSource provides two strings: "hello" and "world".

3. Step 3: Calculate total invocations

   Total = 2 (null and empty) + 2 (hello, world) = 4 test runs.

4. Final Answer:

   4 -> Option A

5. Quick Check:

   2 null/empty + 2 values = 4 [OK]

Hint: Add null and empty plus other values for total tests [OK]

Common Mistakes:

• Counting only @ValueSource inputs
• Counting null and empty as one input
• Forgetting that @NullAndEmptySource adds two inputs

4. Identify the error in the following JUnit test code using @NullAndEmptySource:

@ParameterizedTest
@NullAndEmptySource
void testInput() {
    // test logic
}

medium

A. Cannot use @NullAndEmptySource without @ValueSource

B. Missing parameter in test method to receive input values

C. Incorrect annotation; should use @Test instead of @ParameterizedTest

D. Test method must be static when using @NullAndEmptySource

Solution

1. Step 1: Check method signature

   The test method has no parameters, but @NullAndEmptySource provides inputs that must be accepted.

2. Step 2: Understand parameterized test requirements

   Parameterized test methods must have parameters matching the sources; missing parameter causes error.

3. Final Answer:

   Missing parameter in test method to receive input values -> Option B

4. Quick Check:

   Parameterized test needs method parameter [OK]

Hint: Parameterized tests need method parameters to accept inputs [OK]

Common Mistakes:

• Leaving test method parameterless with @NullAndEmptySource
• Confusing @Test and @ParameterizedTest annotations
• Thinking @NullAndEmptySource requires @ValueSource

5. You want to test a method that processes user input strings, including null and empty values, plus some specific strings. Which annotation combination correctly covers null, empty, and the strings "admin" and "guest" in a single parameterized test?

hard

A. @ParameterizedTest
@NullAndEmptySource
@ValueSource(strings = {"admin", "guest"})

B. @ParameterizedTest
@EmptySource
@ValueSource(strings = {"admin", "guest"})

C. @ParameterizedTest
@NullSource
@ValueSource(strings = {"admin", "guest"})

D. @ParameterizedTest
@ValueSource(strings = {null, "", "admin", "guest"})

Solution

1. Step 1: Identify annotations for null and empty

   @NullAndEmptySource adds both null and empty string automatically.

2. Step 2: Add specific string inputs

   @ValueSource(strings = {"admin", "guest"}) adds the required specific strings.

3. Step 3: Verify combined usage

   Combining @NullAndEmptySource with @ValueSource covers all needed inputs in one test.

4. Final Answer:

   @ParameterizedTest @NullAndEmptySource @ValueSource(strings = {"admin", "guest"}) -> Option A

5. Quick Check:

   Use @NullAndEmptySource plus @ValueSource for all inputs [OK]

Hint: Combine @NullAndEmptySource with @ValueSource for null, empty, and values [OK]

Common Mistakes:

• Using only @EmptySource or @NullSource missing one input
• Trying to put null in @ValueSource strings (not allowed)
• Not combining annotations properly