Absinthe graphql: testing and displaying changeset errors

Hey there, I’m glad you’re using this library!

Let’s take each of your questions in turn.

Testing

The overall approach here is a very common way to do integration level testing. You may also find that the functions you build to handle the resolvers need unit testing if they’re more complex, but often complexity there gets extracted into service type functions that you’d want to unit test anyway.

A couple of things however would make the testing code you have a bit more idiomatic. Most of these things are phoenix conn test related, there isn’t much absinthe specific about this method of testing.

• use |> post("/api", query_doc) instead of directly setting :body_params
• parse the response body into JSON to look for the value you want instead of using String.contains?. This is particularly important because GraphQL does not use HTTP status codes to indicate errors that may happen on a given field. So for example suppose your account field returned an error "No account found for email hey@you.com". Your tests would actually pass right now, but clearly there’d be an error.

There’s also a few minor things about the testing here that are a bit confusing. Where does the conn part of info.conn come from? What content type header is being set? Why is the :host value being set? Are you using phoenix or just bare plug.

Error handling

It’s definitely common to want to handle changeset errors in a generic way, and definitely noto something you want to have to call explicitly in your resolvers over and over again.

The best solution at the moment is to build a wrapper function that handles this possible return value from the resolver function its wrapping. Here’s an example:

# in your field
resolve handle_errors(&SomeResolver.function/2)

# in your schema module somewhere, or imported thereinto
def handle_errors(fun) do
  fn source, args, info ->
    case Absinthe.Resolution.call(fun, source, args, info) do
      {:error, %Ecto.Changeset{} = changeset} -> format_changeset(changeset)
      val -> val
    end
  end
end

Now all that you have to do is wrap resolvers where you want changesets to be handled in a handle_errors call and you’re good to go. Having to still manually place handle_errors throughout your schema is a bit of an annoyance as well, and so we’re working to finalize a middleware pattern that will let you apply this pattern in an even more generic way. Until then, wrapper functions are the way to go.

Thanks for the answers @benwilson512! They were both very helpful =)

I’ll use that wrapper function and I’m going to have another go at that test to clean up the naming problems and confusing code. Thanks for pointing those things out as I wasn’t sure how far off I was from the right track.

Okay - I’ve revised the test. Here’s what it looks like now if anyone is interested. Thanks again @benwilson512

  @account %{email: "hey@you.com", password: "herewego"}

  setup do
    {:ok, account} = AccountResolver.create(@account, %{})
    {:ok, token} = AccountResolver.login(@account, %{})

    conn = build_conn()
        |> put_req_header("authorization", "Bearer #{token.token}")
        |> put_req_header("content-type", "application/json")

    {:ok, %{conn: conn, id: account.id}}
  end

  defp query_skeleton(query, query_name) do
    %{
      "operationName" => "#{query_name}",
      "query" => "query #{query_name} #{query}",
      "variables" => "{}"
    }
  end

  test "Logged in user should be able to see their email", context do
    query = """
      {
        account (id: #{context.id}) {
          email
        }
      }
    """

    res = context.conn
        |> post("/api", query_skeleton(query, "account"))

    assert json_response(res, 200)["data"]["account"]["email"] == "hey@you.com"
  end

  test "Logged in user should not be able to see their password", context do
    query = """
      {
        account (id: #{context.id}) {
          password
        }
      }
    """

    res = context.conn
        |> post("/api", query_skeleton(query, "account"))

    assert hd(json_response(res, 400)["errors"])["message"]
      == "Cannot query field \"password\" on type \"Account\"."
  end

this solution worked well for me based on brian’s answer

  def handle_errors(fun) do
    fn source, args, info ->
      case Absinthe.Resolution.call(fun, source, args, info) do
        {:error, %Ecto.Changeset{} = changeset} -> format_changeset(changeset)
        val -> val
      end
    end
  end

  def format_changeset(changeset) do
    #{:error, [email: {"has already been taken", []}]}
    errors = changeset.errors
      |> Enum.map(fn({key, {value, context}}) -> 
           [message: "#{key} #{value}", details: context]
         end)
    {:error, errors}
  end

I just wanted to say thanks to @gdub01 for asking about this and the answers that came from it. I am incredibly new to Elixir, GraphQL, and Absinthe and this helped a lot.

I’ve written up what I did in order to test both queries and mutations. Testing Absinthe with ExUnit.

The main difference is that the query param you send needs to look slightly different, these are the two helpers I came up with based on what was shared here before;

def mutation_skeleton(query) do
  %{
    "operationName" => "",
    "query" => "#{query}",
    "variables" => ""
  }
end

def query_skeleton(query, query_name) do
  %{
    "operationName" => "#{query_name}",
    "query" => "query #{query_name} #{query}",
    "variables" => "{}"
  }
end

This is cool

I havn’t written any integration tests at the phoenix level for my graphql endpoint so this’ll be helpful when I get there.

Self Plug: I test my queries one level down using Kronky

So like

query = "{ user(id: \"1\")
  {
    firstName
    lastName
    age
  }
}
"
{:ok, %{data: data}} = evaluate_graphql(query)

user_fields = %{first_name: :string, last_name: string, age: integer}
expected = %User{first_name: "Lilo", last_name: "Pelekai", age: 6}
%{"user" => result} = data
assert_equivalent_graphql(expected, result, user_fields)

I highly recommend making use of variables within test, at least for any complicated input. It means you don’t have to worry about escaping stuff within the query string.

First of all, thank you @benwilson512 and the Absinthe team for your work!

What do you think about bypassing conn using Absinthe.run like so?:

test "query for a post by its ID" do
  {:ok, result} =
    """
    {
      post(id: 42) {
        title
        body
      }
    }
    """
    |> Absinthe.run(Blog.Schema)

  assert result == %{
    data: %{
      "post" => %{
        "title" => "Lorem ipsum",
        "body" => "Lorem ipsum dolor sit amet, consectetur adipiscing elit"
      }
    }
  }
end

It’s an option, but I’m not sure it really brings anything to the table. If you want something more like a unit test I’d focus on unit testing whatever business logic function gets called within specific resolvers. For integration level tests this leaves out stuff that can be important like authorization, or any custom phases specified on the plug.

Good points. Thank you so much!