Support STI and inheritance(with test)

lib/stateful_enum/machine.rb

@@ -54,7 +54,7 @@ def initialize(model, column, states, prefix, suffix, name, &block)
             if to && (!condition || instance_exec(&condition))
               #TODO transaction?
               run_callbacks new_method_name do
-                original_method = self.class.send(:_enum_methods_module).instance_method "#{prefix}#{to}#{suffix}!"
+                original_method = self.class.base_class.send(:_enum_methods_module).instance_method "#{prefix}#{to}#{suffix}!"
                 original_method.bind(self).call
               end
             else

test/dummy/app/models/special_bug.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class SpecialBug < Bug
+end

test/dummy/db/migrate/20160307203948_create_bugs.rb

@@ -8,6 +8,7 @@ def change
       t.integer :status, default: 0
       t.integer :assigned_to_id
       t.datetime :resolved_at
+      t.string :type
 
       t.timestamps null: false
     end

test/mechanic_machine_test.rb

@@ -11,6 +11,14 @@ def test_transition
     assert_equal 'assigned', bug.status
   end
 
+  def test_transition_to_sti
+    special_bug = SpecialBug.new
+    assert_equal 'unassigned', special_bug.status
+    special_bug.assigned_to = User.create!(name: 'user 1')
+    special_bug.assign
+    assert_equal 'assigned', special_bug.status
+  end
+
   def test_transition!
     bug = Bug.new
     bug.assigned_to = User.create!(name: 'user 1')