diff --git a/activemodel/spec/observing_spec.rb b/activemodel/spec/observing_spec.rb
deleted file mode 100644
index 1919bb5991..0000000000
--- a/activemodel/spec/observing_spec.rb
+++ /dev/null
@@ -1,120 +0,0 @@
-require File.join(File.dirname(__FILE__), 'spec_helper')
-
-class ObservedModel < ActiveModel::Base
-  class Observer
-  end
-end
-
-class FooObserver < ActiveModel::Observer
-  class << self
-    public :new
-  end
-  
-  attr_accessor :stub
-
-  def on_spec(record)
-    stub.event_with(record) if stub
-  end
-end
-
-class Foo < ActiveModel::Base
-end
-
-module ActiveModel
-  describe Observing do
-    before do
-      ObservedModel.observers.clear
-    end
-
-    it "initializes model with no cached observers" do
-      ObservedModel.observers.should be_empty
-    end
-    
-    it "stores cached observers in an array" do
-      ObservedModel.observers << :foo
-      ObservedModel.observers.should include(:foo)
-    end
-    
-    it "flattens array of assigned cached observers" do
-      ObservedModel.observers = [[:foo], :bar]
-      ObservedModel.observers.should include(:foo)
-      ObservedModel.observers.should include(:bar)
-    end
-    
-    it "instantiates observer names passed as strings" do
-      ObservedModel.observers << 'foo_observer'
-      FooObserver.should_receive(:instance)
-      ObservedModel.instantiate_observers
-    end
-    
-    it "instantiates observer names passed as symbols" do
-      ObservedModel.observers << :foo_observer
-      FooObserver.should_receive(:instance)
-      ObservedModel.instantiate_observers
-    end
-    
-    it "instantiates observer classes" do
-      ObservedModel.observers << ObservedModel::Observer
-      ObservedModel::Observer.should_receive(:instance)
-      ObservedModel.instantiate_observers
-    end
-    
-    it "should pass observers to subclasses" do
-      FooObserver.instance
-      bar = Class.new(Foo)
-      bar.count_observers.should == 1
-    end
-  end
-  
-  describe Observer do
-    before do
-      ObservedModel.observers = :foo_observer
-      FooObserver.models = nil
-    end
-
-    it "guesses implicit observable model name" do
-      FooObserver.observed_class_name.should == 'Foo'
-    end
-
-    it "tracks implicit observable models" do
-      instance = FooObserver.new
-      instance.send(:observed_classes).should     include(Foo)
-      instance.send(:observed_classes).should_not include(ObservedModel)
-    end
-    
-    it "tracks explicit observed model class" do
-      FooObserver.new.send(:observed_classes).should_not include(ObservedModel)
-      FooObserver.observe ObservedModel
-      instance = FooObserver.new
-      instance.send(:observed_classes).should include(ObservedModel)
-    end
-    
-    it "tracks explicit observed model as string" do
-      FooObserver.new.send(:observed_classes).should_not include(ObservedModel)
-      FooObserver.observe 'observed_model'
-      instance = FooObserver.new
-      instance.send(:observed_classes).should include(ObservedModel)
-    end
-    
-    it "tracks explicit observed model as symbol" do
-      FooObserver.new.send(:observed_classes).should_not include(ObservedModel)
-      FooObserver.observe :observed_model
-      instance = FooObserver.new
-      instance.send(:observed_classes).should include(ObservedModel)
-    end
-    
-    it "calls existing observer event" do
-      foo = Foo.new
-      FooObserver.instance.stub = stub!(:stub)
-      FooObserver.instance.stub.should_receive(:event_with).with(foo)
-      Foo.send(:changed)
-      Foo.send(:notify_observers, :on_spec, foo)
-    end
-    
-    it "skips nonexistent observer event" do
-      foo = Foo.new
-      Foo.send(:changed)
-      Foo.send(:notify_observers, :whatever, foo)
-    end
-  end
-end
\ No newline at end of file
diff --git a/activemodel/spec/spec_helper.rb b/activemodel/spec/spec_helper.rb
deleted file mode 100644
index 004fdfca07..0000000000
--- a/activemodel/spec/spec_helper.rb
+++ /dev/null
@@ -1,17 +0,0 @@
-ENV['LOG_NAME'] = 'spec'
-$LOAD_PATH << File.join(File.dirname(__FILE__), '..', 'vendor', 'rspec', 'lib')
-$LOAD_PATH << File.join(File.dirname(__FILE__), '..', 'lib')
-require 'active_model'
-begin
-  require 'spec'
-rescue LoadError
-  require 'rubygems'
-  require 'spec'
-end
-
-begin
-  require 'ruby-debug'
-  Debugger.start
-rescue LoadError
-  # you do not know the ways of ruby-debug yet, what a shame
-end
\ No newline at end of file
diff --git a/activemodel/test/observing_test.rb b/activemodel/test/observing_test.rb
new file mode 100644
index 0000000000..37291ae4c6
--- /dev/null
+++ b/activemodel/test/observing_test.rb
@@ -0,0 +1,123 @@
+require File.join(File.dirname(__FILE__), 'test_helper')
+
+class ObservedModel < ActiveModel::Base
+  class Observer
+  end
+end
+
+class FooObserver < ActiveModel::Observer
+  class << self
+    public :new
+  end
+  
+  attr_accessor :stub
+
+  def on_spec(record)
+    stub.event_with(record) if stub
+  end
+end
+
+class Foo < ActiveModel::Base
+end
+
+class ObservingTest < ActiveSupport::TestCase
+  def setup
+    ObservedModel.observers.clear
+  end
+
+  test "initializes model with no cached observers" do
+    assert ObservedModel.observers.empty?, "Not empty: #{ObservedModel.observers.inspect}"
+  end
+  
+  test "stores cached observers in an array" do
+    ObservedModel.observers << :foo
+    assert ObservedModel.observers.include?(:foo), ":foo not in #{ObservedModel.observers.inspect}"
+  end
+  
+  test "flattens array of assigned cached observers" do
+    ObservedModel.observers = [[:foo], :bar]
+    assert ObservedModel.observers.include?(:foo), ":foo not in #{ObservedModel.observers.inspect}"
+    assert ObservedModel.observers.include?(:bar), ":bar not in #{ObservedModel.observers.inspect}"
+  end
+
+  uses_mocha "observer instantiation" do
+    test "instantiates observer names passed as strings" do
+      ObservedModel.observers << 'foo_observer'
+      FooObserver.expects(:instance)
+      ObservedModel.instantiate_observers
+    end
+  
+    test "instantiates observer names passed as symbols" do
+      ObservedModel.observers << :foo_observer
+      FooObserver.expects(:instance)
+      ObservedModel.instantiate_observers
+    end
+  
+    test "instantiates observer classes" do
+      ObservedModel.observers << ObservedModel::Observer
+      ObservedModel::Observer.expects(:instance)
+      ObservedModel.instantiate_observers
+    end
+  end
+  
+  test "passes observers to subclasses" do
+    FooObserver.instance
+    bar = Class.new(Foo)
+    assert_equal Foo.count_observers, bar.count_observers
+  end
+end
+  
+class ObserverTest < ActiveSupport::TestCase
+  def setup
+    ObservedModel.observers = :foo_observer
+    FooObserver.models = nil
+  end
+
+  test "guesses implicit observable model name" do
+    assert_equal 'Foo', FooObserver.observed_class_name
+  end
+
+  test "tracks implicit observable models" do
+    instance = FooObserver.new
+    assert  instance.send(:observed_classes).include?(Foo), "Foo not in #{instance.send(:observed_classes).inspect}"
+    assert !instance.send(:observed_classes).include?(ObservedModel), "ObservedModel in #{instance.send(:observed_classes).inspect}"
+  end
+  
+  test "tracks explicit observed model class" do
+    old_instance = FooObserver.new
+    assert !old_instance.send(:observed_classes).include?(ObservedModel), "ObservedModel in #{old_instance.send(:observed_classes).inspect}"
+    FooObserver.observe ObservedModel
+    instance = FooObserver.new
+    assert instance.send(:observed_classes).include?(ObservedModel), "ObservedModel not in #{instance.send(:observed_classes).inspect}"
+  end
+  
+  test "tracks explicit observed model as string" do
+    old_instance = FooObserver.new
+    assert !old_instance.send(:observed_classes).include?(ObservedModel), "ObservedModel in #{old_instance.send(:observed_classes).inspect}"
+    FooObserver.observe 'observed_model'
+    instance = FooObserver.new
+    assert instance.send(:observed_classes).include?(ObservedModel), "ObservedModel not in #{instance.send(:observed_classes).inspect}"
+  end
+  
+  test "tracks explicit observed model as symbol" do
+    old_instance = FooObserver.new
+    assert !old_instance.send(:observed_classes).include?(ObservedModel), "ObservedModel in #{old_instance.send(:observed_classes).inspect}"
+    FooObserver.observe :observed_model
+    instance = FooObserver.new
+    assert instance.send(:observed_classes).include?(ObservedModel), "ObservedModel not in #{instance.send(:observed_classes).inspect}"
+  end
+  
+  test "calls existing observer event" do
+    foo = Foo.new
+    FooObserver.instance.stub = stub
+    FooObserver.instance.stub.expects(:event_with).with(foo)
+    Foo.send(:changed)
+    Foo.send(:notify_observers, :on_spec, foo)
+  end
+  
+  test "skips nonexistent observer event" do
+    foo = Foo.new
+    Foo.send(:changed)
+    Foo.send(:notify_observers, :whatever, foo)
+  end
+end
\ No newline at end of file
diff --git a/activemodel/test/test_helper.rb b/activemodel/test/test_helper.rb
new file mode 100644
index 0000000000..8e608fa0bc
--- /dev/null
+++ b/activemodel/test/test_helper.rb
@@ -0,0 +1,23 @@
+$:.unshift "#{File.dirname(__FILE__)}/../lib"
+$:.unshift File.dirname(__FILE__)
+
+require 'test/unit'
+require 'active_model'
+require 'active_support/callbacks' # needed by ActiveSupport::TestCase
+require 'active_support/test_case'
+
+def uses_gem(gem_name, test_name, version = '> 0')
+  require 'rubygems'
+  gem gem_name.to_s, version
+  require gem_name.to_s
+  yield
+rescue LoadError
+  $stderr.puts "Skipping #{test_name} tests. `gem install #{gem_name}` and try again."
+end
+
+# Wrap tests that use Mocha and skip if unavailable.
+unless defined? uses_mocha
+  def uses_mocha(test_name, &block)
+    uses_gem('mocha', test_name, '>= 0.5.5', &block)
+  end
+end