Setting up data for Mockito - spring

Question

I am unit testing my spring Rest API and I have had joy mocking my create and retrieve methods using the following structure.
#Test
public void getAllUsersReturnsAListOfAllTheUsersInJSONFormat() throws Exception {
List<User> users = new ArrayList<>();
users.add(new User("DelBoy"));
users.add(new User("Rodney_Trotter"));
users.add(new User("Uncle.Albert"));
Mockito.when(service.getAllUsers()).thenReturn(users);
mvc.perform(get("/api/users"))
.andExpect(status().isOk())
.andExpect(jsonPath("$", Matchers.hasSize(3)))
.andExpect(jsonPath("$[0].username", Matchers.equalTo("DelBoy")))
.andExpect(jsonPath("$[1].username", Matchers.equalTo("Rodney_Trotter")))
.andExpect(jsonPath("$[2].username", Matchers.equalTo("Uncle.Albert")));
}
However, I am trying to create a test for my Update and Delete methods. When I mock the methods they never behave as expected because there is no data to update or delete. After extensive research online I cannot find any information pointing to resolving this issue. My current attempt is the following code.
#Test
public void updateUserUpdatesAUserUponSuccess() throws Exception {
User updatedUser = new User(UUID.fromString("da3f6cae-9126-407b-a1ea-093bdac72434"), "Trigger");
Mockito.when(service.updateUser(updatedUser)).thenReturn(true);
Mockito.when(validator.validateUsername(updatedUser.getUsername())).thenReturn(true);
Mockito.when(validator.validateUUID(updatedUser.getUserId().toString())).thenReturn(true);
String str = mvc.perform(put("/api/users/da3f6cae-9126-407b-a1ea-093bdac72434/TriggersBroom"))
.andExpect(status().isOk()).andReturn().getResponse().getContentAsString();
System.out.println(str);
}
I am not sure how to have user data mocked so that when I make a PUT request it can update the user at the hex Id specified to a different username ("trigger" being the username). How I would like this to work is to have a small set of user objects that I can update when I mock my updateUser function so I can test the update user route actually updates a record. Currently it returns false because nothing is being updated but it should return true as I have tested manually in my development environment outside of unit testing and it works.
Note:
The println was my was of checking what was actually returned and it was false.

Answer 1

How I would like this to work is to have a small set of user objects that I can update when I mock my updateUser function so I can test the update user route actually updates a record
This is because you write:
User updatedUser = new User(UUID.fromString("da3f6cae-9126-407b-a1ea-093bdac72434"), "Trigger");
Mockito.when(service.updateUser(updatedUser)).thenReturn(true);
Then you can see the updatedUser is not the same instance as the one you gonna call in the real service, it's just a instance you created above.
To mock this, you have 2 ways:
If you can get the exactly same instance as the one you gonna call in real service, it will return true for you.
You can use Mockito.eq(updatedUser) to mock. E.g. Mockito.when(service.updateUser(Mockito.eq(updatedUser))).thenReturn(true);
But then you need to remember to override the equals() method for class User. Then if you modify the method equals(), you need to update hashCode() as well