Allow observers to be enabled and disabled.

This is useful in situations like model unit tests and the occasional rake task to backfill old data.

activemodel/test/cases/observer_array_test.rb

@@ -0,0 +1,122 @@
+require 'cases/helper'
+require 'models/observers'
+
+class ObserverArrayTest < ActiveModel::TestCase
+  def teardown
+    ORM.observers.enable :all
+    Budget.observers.enable :all
+    Widget.observers.enable :all
+  end
+
+  def assert_observer_notified(model_class, observer_class)
+    observer_class.instance.before_save_invocations.clear
+    model_instance = model_class.new
+    model_instance.save
+    assert_equal [model_instance], observer_class.instance.before_save_invocations
+  end
+
+  def assert_observer_not_notified(model_class, observer_class)
+    observer_class.instance.before_save_invocations.clear
+    model_instance = model_class.new
+    model_instance.save
+    assert_equal [], observer_class.instance.before_save_invocations
+  end
+
+  test "all observers are enabled by default" do
+    assert_observer_notified Widget, WidgetObserver
+    assert_observer_notified Budget, BudgetObserver
+    assert_observer_notified Widget, AuditTrail
+    assert_observer_notified Budget, AuditTrail
+  end
+
+  test "can disable individual observers using a class constant" do
+    ORM.observers.disable WidgetObserver
+
+    assert_observer_not_notified Widget, WidgetObserver
+    assert_observer_notified     Budget, BudgetObserver
+    assert_observer_notified     Widget, AuditTrail
+    assert_observer_notified     Budget, AuditTrail
+  end
+
+  test "can disable individual observers using a symbol" do
+    ORM.observers.disable :budget_observer
+
+    assert_observer_notified     Widget, WidgetObserver
+    assert_observer_not_notified Budget, BudgetObserver
+    assert_observer_notified     Widget, AuditTrail
+    assert_observer_notified     Budget, AuditTrail
+  end
+
+  test "can disable all observers using :all" do
+    ORM.observers.disable :all
+
+    assert_observer_not_notified Widget, WidgetObserver
+    assert_observer_not_notified Budget, BudgetObserver
+    assert_observer_not_notified Widget, AuditTrail
+    assert_observer_not_notified Budget, AuditTrail
+  end
+
+  test "can disable observers on individual models without affecting observers on other models" do
+    Widget.observers.disable :all
+
+    assert_observer_not_notified Widget, WidgetObserver
+    assert_observer_notified     Budget, BudgetObserver
+    assert_observer_not_notified Widget, AuditTrail
+    assert_observer_notified     Budget, AuditTrail
+  end
+
+  test "can disable observers for the duration of a block" do
+    yielded = false
+    ORM.observers.disable :budget_observer do
+      yielded = true
+      assert_observer_notified     Widget, WidgetObserver
+      assert_observer_not_notified Budget, BudgetObserver
+      assert_observer_notified     Widget, AuditTrail
+      assert_observer_notified     Budget, AuditTrail
+    end
+
+    assert yielded
+    assert_observer_notified Widget, WidgetObserver
+    assert_observer_notified Budget, BudgetObserver
+    assert_observer_notified Widget, AuditTrail
+    assert_observer_notified Budget, AuditTrail
+  end
+
+  test "can enable observers for the duration of a block" do
+    yielded = false
+    Widget.observers.disable :all
+
+    Widget.observers.enable :all do
+      yielded = true
+      assert_observer_notified Widget, WidgetObserver
+      assert_observer_notified Budget, BudgetObserver
+      assert_observer_notified Widget, AuditTrail
+      assert_observer_notified Budget, AuditTrail
+    end
+
+    assert yielded
+    assert_observer_not_notified Widget, WidgetObserver
+    assert_observer_notified     Budget, BudgetObserver
+    assert_observer_not_notified Widget, AuditTrail
+    assert_observer_notified     Budget, AuditTrail
+  end
+
+  test "raises an appropriate error when a developer accidentally enables or disables the wrong class (i.e. Widget instead of WidgetObserver)" do
+    assert_raise ArgumentError do
+      ORM.observers.enable :widget
+    end
+
+    assert_raise ArgumentError do
+      ORM.observers.enable Widget
+    end
+
+    assert_raise ArgumentError do
+      ORM.observers.disable :widget
+    end
+
+    assert_raise ArgumentError do
+      ORM.observers.disable Widget
+    end
+  end
+end
+

activemodel/test/cases/observing_test.rb

@@ -43,6 +43,11 @@ class ObservingTest < ActiveModel::TestCase
     assert ObservedModel.observers.include?(:bar), ":bar not in #{ObservedModel.observers.inspect}"
   end
 
+  test "uses an ObserverArray so observers can be disabled" do
+    ObservedModel.observers = [:foo, :bar]
+    assert ObservedModel.observers.is_a?(ActiveModel::ObserverArray)
+  end
+
   test "instantiates observer names passed as strings" do
     ObservedModel.observers << 'foo_observer'
     FooObserver.expects(:instance)

activemodel/test/models/observers.rb

@@ -0,0 +1,27 @@
+class ORM
+  include ActiveModel::Observing
+
+  def save
+    notify_observers :before_save
+  end
+
+  class Observer < ActiveModel::Observer
+    def before_save_invocations
+      @before_save_invocations ||= []
+    end
+
+    def before_save(record)
+      before_save_invocations << record
+    end
+  end
+end
+
+class Widget < ORM; end
+class Budget < ORM; end
+class WidgetObserver < ORM::Observer; end
+class BudgetObserver < ORM::Observer; end
+class AuditTrail < ORM::Observer
+  observe :widget, :budget
+end
+
+ORM.instantiate_observers