Add spec for NullDataloader#run_isolated

Author: rmosolgo

spec/graphql/dataloader/null_dataloader_spec.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+require "spec_helper"
+
+describe "GraphQL NullDataloader" do
+  it "can run_isolated with previously-captured blocks that register lazies" do
+    dl = GraphQL::Dataloader::NullDataloader.new
+    result = 0
+    dl.run_isolated {
+      lazy = GraphQL::Execution::Lazy.new { result = 100 }
+      dl.lazy_at_depth(1, lazy)
+    }
+    assert_equal 100, result
+  end
+end