add a test for current behavior of errors

test/active_resource/json_errors_test.rb

@@ -0,0 +1,17 @@
+require 'test_helper'
+
+module ActiveResource
+  class JsonErrorsTest < Test::Unit::TestCase
+
+    def test_parsing_of_error_json_hash
+      errors = some_error.from_json({errors: {name: ['missing']}}.to_json)
+      assert_equal({"name"=>["missing"]}, errors)
+    end
+
+    private
+
+    def some_error
+      ActiveResource::Errors.new(ShopifyAPI::Order.new)
+    end
+  end
+end