@NullSource and @EmptySource in JUnit - Test Execution Trace

Test Overview

This test checks a method that processes strings. It verifies the method handles null and empty string inputs correctly by using @NullSource and @EmptySource annotations in JUnit.

Test Code - JUnit 5

JUnit

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.NullSource;
import org.junit.jupiter.params.provider.EmptySource;
import static org.junit.jupiter.api.Assertions.*;

public class StringProcessorTest {

    @ParameterizedTest
    @NullSource
    @EmptySource
    void testProcessStringHandlesNullAndEmpty(String input) {
        StringProcessor processor = new StringProcessor();
        String result = processor.process(input);
        assertEquals("default", result);
    }
}

class StringProcessor {
    public String process(String input) {
        if (input == null || input.isEmpty()) {
            return "default";
        }
        return input.trim();
    }
}

Execution Trace - 2 Steps

Step	Action	System State	Assertion	Result
1	Test starts with input = null from @NullSource	Test environment initialized, no UI involved	Check if process(null) returns "default"	PASS
2	Test runs with input = "" (empty string) from @EmptySource	Test environment ready for next input	Check if process("") returns "default"	PASS

Failure Scenario

Failing Condition: Method process does not return "default" for null or empty input

Execution Trace Quiz - 3 Questions

What inputs does this test method check?

A only empty string

B null and empty string

C only null

D random strings

Key Result

Using @NullSource and @EmptySource together in parameterized tests helps verify that methods handle null and empty inputs gracefully, which are common edge cases.