@NullAndEmptySource in JUnit

Introduction

@NullAndEmptySource helps you test how your code handles empty or null inputs easily. It saves time by automatically providing these special cases to your test method.

When you want to check if your method works correctly with null input.

When you want to verify behavior with empty strings or collections.

When you want to avoid writing separate tests for null and empty values.

When you want to improve test coverage for edge cases.

When you want to catch bugs caused by missing or empty data.

Syntax

JUnit

@NullAndEmptySource

Use this annotation on a parameterized test method.

It automatically adds null and empty values as test inputs.

Examples

This test runs twice: once with null and once with an empty string.

JUnit

@ParameterizedTest
@NullAndEmptySource
void testWithNullAndEmpty(String input) {
    assertTrue(input == null || input.isEmpty());
}

This test checks behavior for null and empty lists.

JUnit

import java.util.List;

@ParameterizedTest
@NullAndEmptySource
void testListInput(List<String> list) {
    assertTrue(list == null || list.isEmpty());
}

Sample Program

This test method runs twice automatically: once with null and once with an empty string. It checks that the input is either null or empty.

JUnit

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

public class ExampleTest {

    @ParameterizedTest
    @NullAndEmptySource
    void testStringIsNullOrEmpty(String input) {
        assertTrue(input == null || input.isEmpty());
    }
}

Important Notes

@NullAndEmptySource works only with parameterized tests.

It can be combined with other sources like @ValueSource for more inputs.

It helps catch bugs early by testing edge cases you might forget.

Summary

@NullAndEmptySource adds null and empty values to your tests automatically.

It is useful for testing how code handles missing or empty inputs.

Use it with @ParameterizedTest to save time and improve coverage.

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