added tests, replaced classify with constantize - using classify here cuts the last 's' in ORM name

railties/lib/rails/generators/resource_helpers.rb

@@ -64,7 +64,7 @@ def orm_class
             end
 
             begin
-              "#{options[:orm].to_s.classify}::Generators::ActiveModel".constantize
+              "#{options[:orm].to_s.camelize}::Generators::ActiveModel".constantize
             rescue NameError
               Rails::Generators::ActiveModel
             end

railties/test/generators/orm_test.rb

+require "generators/generators_test_helper"
+require "rails/generators/rails/scaffold_controller/scaffold_controller_generator"
+
+# Mock out two ORMs
+module ORMWithGenerators
+  module Generators
+    class ActiveModel
+      def initialize(name)
+      end
+    end
+  end
+end
+
+module ORMWithoutGenerators
+  # No generators
+end
+
+class OrmTest < Rails::Generators::TestCase
+  include GeneratorsTestHelper
+  tests Rails::Generators::ScaffoldControllerGenerator
+
+  def test_orm_class_returns_custom_generator_if_supported_custom_orm_set
+    g = generator ["Foo"], :orm => "ORMWithGenerators"
+    assert_equal ORMWithGenerators::Generators::ActiveModel, g.send(:orm_class)
+  end
+
+  def test_orm_class_returns_rails_generator_if_unsupported_custom_orm_set
+    g = generator ["Foo"], :orm => "ORMWithoutGenerators"
+    assert_equal Rails::Generators::ActiveModel, g.send(:orm_class)
+  end
+
+  def test_orm_instance_returns_orm_class_instance_with_name
+    g = generator ["Foo"]
+    orm_instance = g.send(:orm_instance)
+    assert g.send(:orm_class) === orm_instance
+    assert_equal "foo", orm_instance.name
+  end
+end