为什么Java代码未显示适当数量的实例？

Question

我在freecodecamp上关注Java tutorial，并编写了以下代码。在这里，我创建了两个类：PersonTest.java和Person.java。我在PersonTest.java中编写了3个测试。在编写前两个测试时，已经创建了Person类的两个实例。在第三个测试中，它计算创建的实例数；我得到的输出为1（我希望它是2）。我不明白为什么会这样显示。任何帮助表示赞赏：）

PersonTest.java

package com.atharvajoshi.javacourse.lesson2;
import static org.junit.Assert.assertEquals;
import org.junit.Test;

public class PersonTest {
    @Test
    public void shouldReturnHelloWorld() {
        Person atharva = new Person();                  // First instance
        assertEquals("Hello World", atharva.helloworld());
    }

    @Test
    public void shouldReturnHelloAtharva() {
        Person person = new Person();                   // Second instance
        assertEquals("Hello Atharva", person.hello("Atharva"));
    }


    @Test
    public void shouldReturnNumberOfPersons() {
        System.out.println(Person.numberOfPersons());   // Answer is coming to be 1
        assertEquals(2, Person.numberOfPersons());      // Test failed
    }
}

Person.java

package com.atharvajoshi.javacourse.lesson2;

public class Person {

    private static int personCounter = 0;

    public Person() {
        personCounter ++;
    }

    public String helloworld() {
        return "Hello World";
    }

    public String hello(String anyName) {
        return "Hello " + anyName;
    }

    public static int numberOfPersons() {
        return personCounter;
    }
}

输出：1

Output