Add test for each way of using a query_string

Author: xuorig

spec/graphql/query_spec.rb

@@ -45,7 +45,7 @@
   let(:result) { query.result }
 
   describe "when passed both a query string and a document" do
-    it "returns an error to the client" do
+    it "returns an error to the client when query kwarg is used" do
       assert_raises ArgumentError do
         GraphQL::Query.new(
           schema,
@@ -54,6 +54,16 @@
         )
       end
     end
+
+    it "returns an error to the client" do
+      assert_raises ArgumentError do
+        GraphQL::Query.new(
+          schema,
+          "{ fromSource(source: COW) { id } }",
+          document: document
+        )
+      end
+    end
   end
 
   describe "when passed no query string or document" do