Raise when both query string and document are provided to Query

lib/graphql/query.rb

@@ -78,6 +78,10 @@ def initialize(schema, query_string = nil, query: nil, document: nil, context: n
       @query_string = query_string || query
       @document = document
 
+      if @query_string && @document
+        raise ArgumentError, "Query should only be provided a query string or a document, not both."
+      end
+
       # A two-layer cache of type resolution:
       # { abstract_type => { value => resolved_type } }
       @resolved_types_cache = Hash.new do |h1, k1|

spec/graphql/query_spec.rb

@@ -44,6 +44,28 @@
   )}
   let(:result) { query.result }
 
+  describe "when passed both a query string and a document" do
+    it "returns an error to the client when query kwarg is used" do
+      assert_raises ArgumentError do
+        GraphQL::Query.new(
+          schema,
+          query: "{ fromSource(source: COW) { id } }",
+          document: document
+        )
+      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
     it 'returns an error to the client' do
       res = GraphQL::Query.new(