What are the advantages and disadvantages of writing unit tests?

Advantages of unit tests:

• Early detection of errors — tests help identify bugs at early stages of development.
• Code documentation — tests show how the code should work.
• Confidence during refactoring — code changes can be verified for correctness.
• Automation of checks — tests can be run automatically during build.

Disadvantages:

• Time costs for writing and maintaining — writing tests requires resources.
• False sense of security — tests do not cover all cases and may miss errors.
• Complexity of testing some components — for example, UI or integrations.

Example of a simple unit test in Java using JUnit:

import static org.junit.Assert.*;
import org.junit.Test;

public class CalculatorTest {
    @Test
    public void testAdd() {
        Calculator calc = new Calculator();
        assertEquals(5, calc.add(2, 3));
    }
}

Unit tests are an important tool for improving code quality but require a reasonable approach.