What types of tests do you usually create and what is each of them intended for?

I usually create the following types of tests:

• Unit tests: check individual methods or classes to ensure they work correctly in isolation.
• Integration tests: verify the interaction between multiple components or layers of the application.
• Functional tests: ensure the system performs business functions according to requirements.
• Regression tests: rerun after changes to ensure that existing functionality has not broken.

Example of a simple unit test in Java using JUnit:

import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;

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