Mockito，JUnit和Map嵌套在另一个类中

Question

I'm beginner with Mockito and I have problem with creating stub. I have the following interface:

public interface IMsgField {
  public String getName();
  public Object getValue();
}

One class implements above interface as follows

public final class CMsgField implements IMsgField {

  private String name;
  private Object value;

  public CMsgField(String name, Object value) {
   this.name = name;
   this.value = value;
}

 . . .
}

And I have one more class :

class FieldsWrapper {
    private Map<String, IMsgField> fields = new HashMap<String, IMsgField>();

     . . .
    public Map<String, IMsgField> getFields() {
       return fields;
    }
}

I've created the following junit test:

@Test
public void test() {
    FieldsWrapper fieldsWrapper = mock(FieldsWrapper.class);
    stub(fieldsWrapper.getFields()).toReturn(new HashMap<String, IMsgField>());
    stub(fieldsWrapper.getFields().get("id_object")).toReturn(new CMsgField("id_object", "100"));
     . . .
}

And when I ran this test I received the following exception at last line in above test :

org.mockito.exceptions.misusing.WrongTypeOfReturnValue: 
CMsgField cannot be returned by getFields()
getFields() should return Map
...

I don't why, please help me with this problem. Thanks in advance.

Answer 1

I would either mock the Map or use a local variable for it :

@Test
public void test() {
    Map<String, IMsgField> testMap = new HashMap<String, IMsgField>();
    testMap.put("id_object", new CMsgField("id_object", "100"));
    FieldsWrapper fieldsWrapper = mock(FieldsWrapper.class);
    stub(fieldsWrapper.getFields()).toReturn(testMap);
}

Answer 2

You should rather proceed this way:

@Test
public void test() {
    Map<String, IMsgField> stubbedMap = new HashMap<String, IMsgField>();
    stubbedMap.put("id_object", new CMsgField("id_object", "100"));
    FieldsWrapper fieldsWrapper = mock(FieldsWrapper.class);
    stub(fieldsWrapper.getFields()).toReturn(stubbedMap);
}

Because you only have to stub fieldsWrapper.getFields(). testMap.get("id_object") is a method call from Map, which is not stubbed, so it can't work.

Answer 3

You can not do chains of method calls while mocking.

@Test
public void test() {
    FieldsWrapper fieldsWrapper = mock(FieldsWrapper.class);
    HashMap<String, IMsgField>() map = new HashMap<String, IMsgField>();
    map.put("id_object", CMsgField("id_object", "100"));
    stub(fieldsWrapper.getFields()).toReturn(map);    
 . . .
}