public async Task AddFriendRequest_RequestedByUserIsNull_ReturnNotFound()
{
_userService.Setup(us => us.GetUserByIdAsync(It.IsAny <string>())).ReturnsAsync(() => null);
var result = await _friendController.AddFriendRequest(It.IsAny <string>()) as NotFoundResult;
Assert.That(result, Is.TypeOf <NotFoundResult>());
}