我正在使用来自apache commons lang3库的RandomStringUtils类。我在嘲笑它的随机方法时遇到了问题。
下面是我的示例类，它带有简单的方法generatePassword。

public class Example() {

    public String generatePassword() {
       
     final String randomDevicePass = RandomStringUtils.random(10, "abcdefghijklmnopqrstuvwxyz");
     
     System.out.println(randomDevicePass)
    
     return randomDevicePass;
        
    }

}

下面是我的测试类，通过它我正在运行测试用例。

@RunWith(MockitoJUnitRunner.class)
public class ExampleTest() {

    @InjectMocks
    private Example Example;
    
    @Mock
    RandomStringutils randomStringutils;

    @Test
    public void givenCharacters_returnStringPassword() {

           Mockito.when(randomStringUtils.random(Mockito.anyInt(),Mockito.anyString())).thenReturn("asdf");

    Assertions.assertEquals("asdf", example.generatePassword());
    }

}

它给出以下错误：

Misplaced or misused argument matcher detected here:
You cannot use argument matchers outside of verification or stubbing.
Examples of correct usage of argument matchers:
    when(mock.get(anyInt())).thenReturn(null);
    doThrow(new RuntimeException()).when(mock).someVoidMethod(anyObject());
    verify(mock).someMethod(contains("foo"))

This message may appear after an NullPointerException if the last matcher is returning an object 
like any() but the stubbed method signature expect a primitive argument, in this case,
use primitive alternatives.
    when(mock.get(any())); // bad use, will raise NPE
    when(mock.get(anyInt())); // correct usage use

Also, this error might show up because you use argument matchers with methods that cannot be mocked.
Following methods *cannot* be stubbed/verified: final/private/equals()/hashCode().
Mocking methods declared on non-public parent classes is not supported.

org.mockito.exceptions.misusing.InvalidUseOfMatchersException: 
Misplaced or misused argument matcher detected here:

我不知道如何模仿Java内置的apache公共库类。不知道我们能不能用spy？或者别的什么...有人能帮我这个忙吗？
先谢了