Calling non mocked functions for a mocked object

Question

import java.lang.Math;
import static org.mockito.Mockito.*;
import java.util.Map;
import java.util.HashMap;

public class MyClass
{
  class Test {
      int a = 10;
      Test() {}
  }    
  class OtherClass
  {
     public OtherClass()
     {}

     Map<String, Double> f() {
        System.out.print("Just for testing"); 
       return new HashMap<>();
     }

     Test getT() {
         return new Test();
     }

  }

  public static void main(String[] args)
  {
    OtherClass c = mock(OtherClass.class);
    Map<String, Double> test = c.f();
    System.out.println(test.size());
    MyClass.Test t = c.getT();
    System.out.println(t);
  }
}

In this example I have created mock object for OtherClass type. What strange for me that cf() returns empty Map, meanwhile c.getT() returns null. Could you please help me to understand this behavior?

Answer 1

If you do not provide a stub for Map , Mockito will return an empty map. This is a documented feature, confirmed by the JavaDocs :

By default, for all methods that return value, mock returns null, an empty collection or appropriate primitive/primitive wrapper value (eg: 0, false, ... for int/Integer, boolean/Boolean, ...).