Error Test for JSON-based APIs

#file path -> test/not_skull_web/controllers/user_controller_test.exs
#add this code at the indicated place mentioned in comments of test/not_skull_web/controllers/
#user_controller_test.exs in the playground widget
test "error: does not update, returns errors when given invalid attributes",
      %{
        conn_with_token: conn_with_token,  
        user: existing_user
      } do
  conn =
    put(conn_with_token, "/api/users/#{existing_user.id}", %{name: ""})  
  assert body = json_response(conn, 422) 
  user_from_db = Repo.get(User, existing_user.id)
  assert user_from_db == existing_user  
  actual_errors = body["errors"]
  refute Enum.empty?(actual_errors)
  expected_error_keys = ["field", "message"]
  for error <- actual_errors do  
    assert_unordered_lists_are_equal(
      actual: Map.keys(error),
      expected: expected_error_keys
    )
  end
end