对于下面的代码片段，我需要编写JUnit测试用例的帮助。任何解决方案或代码提示都将不胜感激

public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }
    
    public int subtract(int a, int b) {
        return a - b;
    }
}

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

public class CalculatorTest {
    private Calculator calculator = new Calculator();
    
    @Test
    public void testAdd() {
        int result = calculator.add(2, 3);
        assertEquals(5, result);
    }
    
    @Test
    public void testSubtract() {
        int result = calculator.subtract(5, 3);
        assertEquals(2, result);
    }
}