Spy with Mockito - Spy vs Mock

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What is a Spy? How do you spy with Mockito?
Github : github.com/in2...
in28Minutes Course Guide - courses.in28mi...
What You Will Learn during this Step:
- Understand what a Spy does?
- Creating a spy with Mockito?
- Overriding specific methods in a spy?
Code Snippets
import static org.mockito.Mockito.spy;
List listSpy = spy

[@rohitrox8]

I was literally suffering to understand spy by words. Thanks to you now!

[@RamapatiMaurya]

A person can learn more and put more attention if you show him/ her with error cases. Better to do like that way

[@AhmadShahwaiz]

Beautifully explained

[@kekiir]

clear explanation!

[@MaggicBones]

A M A Z I N G !!!

[@umeshkumarroy5804]

Really Great

[@chaitanyabag7348]

Good and comprehensive video

[@maheshbeesetty5979]

Great

[@SanjeevSharma123]

great videos thank you :)

[@shankars4281]

So, when we use mock, we can't do below thing, since we it doesn't creates real object?
List arrayList = mock(ArrayList.class);
arrayList.add("sss");
assertEquals(1,arrayList.size());

[@thegamerz5034]

Yes, when we use Mock, we can't do below thing. This is because to create a stub of a specific method of a class, the return type needs to be the same as the real implementation. List.add() returns a boolean and not a new list with the added object. This makes it so that we can't return a list with "sss" when we do .add for a Mocked arraylist. For example:
//Spy:
//Given
List spyArrayList = Mockito.spy(new ArrayList());
//When
spyArrayList.add("sss");
//Then
assertEquals(1, spyArrayList.size());
// This will return true.
// For a mock, you need to DEFINE a stub
// for each method. Because the logic is gone.
// You have to specifically tell what outcome it should return for a specific input.
//Mock:
//Given
List mockArrayList = Mockito.mock(ArrayList.class);
List listWeWantNack = new ArrayList(List.of("sss"));
//Next line doesn't work, since we can't specify a return type of arraylist,
//because .add expects a boolean back.
//This means we can't return an added list of stuff, because we can't override the .add method of list.
//Mockito.when(mockArrayList.add("sss")).thenReturn(listWeWantNack);
Sidenote:
A Spy gives the same utility as the real implementation as you can see in the example, but you can specifically stub specific methods with a spy. This is quite powerful, since you don't have to specify what to return for every method of a mocked class, unlike a Mock where you have to specify what to return for EVERY method.
This is why a Spy is called "partially mocked".

[@prasannakumarattuluri7650]

its a good tutorial and clear one :)

[@preethikashenoy]

Please add a tutorial on mocking SQLiteDatabase. Thanks in advance.

[@ShahidKhan-qx5fh]

python add is so annoying ....