如何模拟返回返回模拟对象的方法

Question

How to mock a method that returns a mock object which is cast.

I have a method which returns a mock object which is cast from an Object into SomeClass then calls a method on SomeClass .

The problem is the method getBean("SomeClass") returns an Object and not SomeClass so mocking

when(mockApplicationContext.getBean("SomeClass")).thenReturn(mockSomeClass);

dosent work as the return type is wrong and mocking

when(mockApplicationContext.getBean("SomeClass")).thenReturn(mockObject);

dosent work as the method called on SomeClass dosent exist and I cant mock SomeClass .

How can this be mocked?

Method to test.

    public void anyMethod() {       

    // code omitted

    ( (SomeClass) getApplicationContext().getBean("SomeClass") ).someMethod(anArgument);

    // ...
}

Test Method.

@Test
public void testAnyMethod() {

    // ...

    SomeClass mockSomeClass = mock(SomeClass.class);
    when(mockSomeClass.someMethod(anArgument)).thenReturn(someResult);

    ApplicationContext mockApplicationContext = mock(ApplicationContext.class);
    when(mockApplicationContext.getBean("SomeClass")).thenReturn(mockSomeClass);

    PowerMockito.doReturn(mockApplicationContext).when(GetContext.class, "getApplicationContext");

    // ...
}

Answer 1

If you change your method implementation slightly to use the type-safe methods:

public void anyMethod() {       

    // code omitted

    getApplicationContext().getBean("SomeClass", SomeClass.class).someMethod(anArgument);

    // ...
}

then your test class changes only a little to:

@Test
public void testAnyMethod() {

    // ...

    SomeClass mockSomeClass = mock(SomeClass.class);
    when(mockSomeClass).someMethod(anArgument).thenReturn(someResult);

    // The problem is that .getBean("SomeClass") returns Object.class which is then cast
    // to SomeClass in anyMethod. If I return an Object then someMethod(anArgument) dosent exist

    ApplicationContext mockApplicationContext = mock(ApplicationContext.class);
    when(mockApplicationContext.getBean("SomeClass", SomeClass.class)).thenReturn(mockSomeClass);

    // ...
}

Answer 2

Here is a simple example of doing what you want - you need to specify the behaviour of the mocked class during your set up:

ApplicationContext ctx = mock(ApplicationContext.class);
List<String> mockList = mock(List.class);
when(ctx.getBean("XYZ")).thenReturn(mockList);
when(mockList.get(0)).thenReturn("ABC");  // Setting up the behaviour!

// ctx.getBean("XYZ").get(0); // can't call List methods here

// Cast and call in one
System.out.println(((List<String>) ctx.getBean("XYZ")).get(0)); // Prints "ABC"

// .. or cast into a new reference
List<String> list = (List<String>) ctx.getBean("XYZ");
System.out.println(list.get(0));  // Also prints "ABC"