冲刺7

Day 7：


```java
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

public class CalculatorTest {
    private Calculator calculator = new Calculator();

    @Test
    public void testAdd() {
        Assertions.assertEquals(5, calculator.add(2, 3));
    }

    @Test
    public void testSubtract() {
        Assertions.assertEquals(2, calculator.subtract(5, 3));
    }

    @Test
    public void testMultiply() {
        Assertions.assertEquals(10, calculator.multiply(2, 5));
    }

    @Test
    public void testDivide() {
        Assertions.assertEquals(2, calculator.divide(10, 5));
    }
}