Mocking a List and attempting to iterate over it

Question

Currently using Mockito to Test a method from one of my classes. My class contains a List, and the method takes in an object of the same class. The issue is when I attempt to it

Answer 1

As @Adam says: "Iterating over a list using for-each syntax calls Collection.iterator() under the hood. This returns null because you've not setup mockito to return anything else." So you have to setup mockito in this way;

    @Test
public void test_mergeShipments_increasesByOneWhenAShipmentOfOneAddedToAShipmentORderSizeOfTwo(){

      //GIVEN

   //Mock the iterator
    Iterator stockIteratorMock = mock(Iterator.class);

    //WHEN

    //In setUp method you put two objs
    when(mockShipmentOrder.size()).thenReturn(2); 

   //Set a mock for iterator
    when(mockShipmentOrder.iterator()).thenReturn(iteratorMock);

   // Instruct the iteratorMock when stop to return item
    when(iteratorMock.hasNext())
            .thenReturn(true)
            .thenReturn(true)
            .thenReturn(false);

    // Instruct the iteratorMock what obj return on each call
    // You can skip this: mockShipmentOrders.add(mockOrder1);
    when(stockIteratorMock.next())
      .thenReturn(mockOrder1)
      .thenReturn(mockOrder2);

    shipment.mergeShipments(shipment);

    //THEN
    assertEquals(2, shipment.getShipmentOrders().size());
}

This way is verbose, but you are free to modify the behaviour of the array list and also understand how it works under the wood.