DEV: Define theme test modules under a /test subdirectory (#13158)

app/models/theme.rb

@@ -141,7 +141,7 @@ class Theme < ActiveRecord::Base
     SvgSprite.expire_cache
   end
 
-  BASE_COMPILER_VERSION = 50
+  BASE_COMPILER_VERSION = 51
   def self.compiler_version
     get_set_cache "compiler_version" do
       dependencies = [

app/models/theme_field.rb

@@ -151,6 +151,7 @@ class ThemeField < ActiveRecord::Base
 
     js_compiler = ThemeJavascriptCompiler.new(theme_id, theme.name)
     filename, extension = name.split(".", 2)
+    filename = "test/#{filename}" if js_tests_field?
     begin
       case extension
       when "js.es6", "js"