add spec for delivery_adapter

spec/graphql/delivery_adapter_spec.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+RSpec.describe GraphQL::AnyCable::DeliveryAdapter do
+  describe ".lookup" do
+    context "when config.delivery_method is valid" do
+      around do |ex|
+        old_value = GraphQL::AnyCable.config.delivery_method
+        GraphQL::AnyCable.config.delivery_method = :inline
+
+        ex.run
+
+        GraphQL::AnyCable.config.delivery_method = old_value
+      end
+
+      it "returns InlineAdapter" do
+        expect(GraphQL::Adapters::InlineAdapter).to receive(:new).with(executor_object: "object")
+
+        described_class.lookup(executor_object: "object")
+      end
+    end
+
+    context "when config.delivery_method is invalid" do
+      around do |ex|
+        old_value = GraphQL::AnyCable.config.delivery_method
+        GraphQL::AnyCable.config.delivery_method = :unknown_adapter
+
+        ex.run
+
+        GraphQL::AnyCable.config.delivery_method = old_value
+      end
+
+      it "raises an error" do
+        expect { described_class.lookup(executor_object: "object") }.to raise_error(
+          NameError,
+          /Delivery adapter :unknown_adapter haven't been found/,
+        )
+      end
+    end
+  end
+end