public void ChangeUsernameTest()
        {
            //Arrange
            int index    = 0;
            var testUser = GetUserCollection().ElementAt(index);

            //Act
            userMockRepository.Setup(x => x.Get(index.ToString())).Returns(GetUserCollection().ElementAt(index));
            mapper.Setup(x => x.Map <User>(It.IsAny <User>())).Returns(GetUserCollection().ElementAt(index));
            userService.ChangeUsername(testUser, "newname");

            //Assert
            Assert.Equal(testUser.UserName, "newname");
        }