don't perform mute/unmute side effects w/o change

fixes CNVS-21979

particularly, if an assignment is already unmuted, don't trigger "just
unmuted" broadcast events when "unmute!" is called

test-plan:
 - have your account configured to receive unmute notification
 - edit an unmuted assignment in a published course you're enrolled in
 - save it with the "Mute" checkbox still off
 - don't receive an unmute notification

Change-Id: I948b5f1b2176e574ecf43fcde187019d7eadb50d
Reviewed-on: https://gerrit.instructure.com/58788
Reviewed-by: Cody Cutrer <cody@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins
QA-Review: Ben Bolton <bbolton@instructure.com>
Product-Review: Matt Fairbourn <mfairbourn@instructure.com>

Author: lukfugl

lib/mutable.rb

@@ -20,12 +20,14 @@ def declare_mutable_broadcast_policy(options)
   end
 
   def mute!
+    return if muted?
     self.update_attribute(:muted, true)
     clear_sent_messages
     hide_stream_items
   end
 
   def unmute!
+    return unless muted?
     self.update_attribute(:muted, false)
     broadcast_unmute_event
     show_stream_items

spec/lib/mutable_spec.rb

@@ -0,0 +1,76 @@
+#
+# Copyright (C) 2015 Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper.rb')
+
+describe Mutable do
+  before do
+    @klass = Class.new do
+      # the signature that Mutable requires. if we care about side
+      # effects/return values from these methods for specific tests, we'll mock
+      # them
+      def muted?; end
+      def update_attribute(*args); end
+      def save!; end
+
+      include Mutable
+    end
+
+    @mutable = @klass.new
+  end
+
+  describe "mute!" do
+    it "updates if not yet muted" do
+      @mutable.expects(:muted?).returns(false)
+      @mutable.expects(:update_attribute).once.with(:muted, true)
+      @mutable.mute!
+    end
+
+    it "skips update if already muted" do
+      @mutable.expects(:muted?).returns(true)
+      @mutable.expects(:update_attribute).never
+      @mutable.mute!
+    end
+  end
+
+  describe "unmute!" do
+    it "updates if currently muted" do
+      @mutable.expects(:muted?).returns(true)
+      @mutable.expects(:update_attribute).once.with(:muted, false)
+      @mutable.unmute!
+    end
+
+    it "skips update if not muted" do
+      @mutable.expects(:muted?).returns(false)
+      @mutable.expects(:update_attribute).never
+      @mutable.unmute!
+    end
+
+    it "broadcasts unmute event if currently muted" do
+      @mutable.expects(:muted?).returns(true)
+      @mutable.expects(:broadcast_unmute_event).once
+      @mutable.unmute!
+    end
+
+    it "skips unmute event if not muted" do
+      @mutable.expects(:muted?).returns(false)
+      @mutable.expects(:broadcast_unmute_event).never
+      @mutable.unmute!
+    end
+  end
+end