我试图用mockito spy来模拟一个类的示例。我读了这篇博客文章，可能是为了测试所描述的行为是否真实，但它并没有达到我的预期。下面是一个简短的自包含（in）正确示例：

import org.mockito.Mockito;

import static org.mockito.Mockito.doReturn;
import static org.mockito.Mockito.when;

public class Sandbox {

    static class Foo {
        // nothing
    }

    public static class Subject {

        public int doStuffNoParameters() {
            System.out.println("doStuffNoParameters called");
            return -1;
        }

        public int doStuff(Foo f, String s) {
            System.out.println("doStuff called!");
            return 42;
        }
    }

    public static void main(String[] args) {
        Subject s = new Subject();
        final Subject mock = Mockito.spy(s);

        System.out.println((mock.doStuffNoParameters())); // expected doStuffNoParameters , -1
        // mock method with no parameters using when or doReturn
        doReturn(1).when(mock).doStuffNoParameters();
        System.out.println(mock.doStuffNoParameters()); // expected 1
        when(mock.doStuffNoParameters()).thenReturn(1);
        System.out.println(mock.doStuffNoParameters()); // expected 1

        // mock method with no parameters using when or doReturn
        doReturn(1).when(mock).doStuff(Mockito.any(Foo.class), Mockito.anyString());
        System.out.println(mock.doStuff(null, null)); // expected 1, got doStuff called then 42
        when(mock.doStuff(Mockito.any(Foo.class), Mockito.any(String.class))).thenReturn(1); // expected nothing, got doStuffCalled
        System.out.println(mock.doStuff(null, "anyway")); // expected 1; got doStuff called then 42

    }
}

输出为：

doStuffNoParameters called
-1
1
1
doStuff called!
42
doStuff called!
doStuff called!
42

预期输出在代码中。特别是，我想知道，当函数调用的参数可能不可用、来自不同示例或在编写模拟行为时为null时，如何使用参数模拟对函数的调用。使用mockito v2.28.2编辑