properly prepend ProvisioningTemplate class with helper (#28)

fixes error during settings rendering because method is not found

app/models/concerns/foreman_rescue/provisioning_template_extensions.rb

@@ -2,7 +2,7 @@
 
 module ForemanRescue
   module ProvisioningTemplateExtensions
-    def self.templates_by_kind(kind)
+    def templates_by_kind(kind)
       template_kind = TemplateKind.find_by(name: kind)
       ProvisioningTemplate.where(:template_kind => template_kind).pluck(:name, :name).to_h
     end

lib/foreman_rescue/engine.rb

@@ -54,7 +54,7 @@ class Engine < ::Rails::Engine
       Host::Managed.prepend ForemanRescue::HostExtensions
       HostsHelper.prepend ForemanRescue::HostsHelperExtensions
       Nic::Managed.prepend ForemanRescue::Orchestration::TFTP
-      ProvisioningTemplate.prepend ForemanRescue::ProvisioningTemplateExtensions
+      ProvisioningTemplate.singleton_class.prepend ForemanRescue::ProvisioningTemplateExtensions
     rescue StandardError => e
       Rails.logger.warn "ForemanRescue: skipping engine hook (#{e})"
     end

test/models/provisioning_template_test.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require 'test_plugin_helper'
+
+class ProvisioningHostTest < ActiveSupport::TestCase
+  setup do
+    User.current = FactoryBot.build(:user, :admin)
+    disable_orchestration
+  end
+
+  context 'provisioning template query' do
+    context 'with type PXELinux' do
+      let(:type) do
+        'PXELinux'
+      end
+
+      test 'should return templates' do
+        templates = ProvisioningTemplate.templates_by_kind(type)
+
+        assert_includes templates, 'PXE Default Menu'
+        assert_includes templates, 'PXELinux default local boot'
+        assert_includes templates, 'PXELinux global default'
+      end
+    end
+  end
+end