Don't modify a frozen hash.

lib/guard.rb

@@ -16,8 +16,7 @@ module Guard
       @listener = Listener.select_and_init
       @guards   = []
 
-      options[:notify] = false if ENV["GUARD_NOTIFY"] == 'false'
-      options[:notify] ? Notifier.turn_on : Notifier.turn_off
+      !@options[:notify] || ENV["GUARD_NOTIFY"] == 'false' ? Notifier.turn_off : Notifier.turn_on
 
       self
     end
@@ -61,7 +60,7 @@ module Guard
       guard.send(task_to_supervise, *args)
     rescue Exception
       UI.error("#{guard.class.name} guard failed to achieve its <#{task_to_supervise.to_s}> command: #{$!}")
-      ::Guard.guards.delete guard
+      guards.delete guard
       UI.info("Guard #{guard.class.name} has just been fired")
       return $!
     end

spec/guard/notifier_spec.rb

@@ -38,14 +38,14 @@ describe Guard::Notifier do
   end
 
   describe ".turn_off" do
+    before(:each) { subject.turn_off }
+    
     if mac? && growl_installed?
       it "does nothing" do
         Growl.should_not_receive(:notify)
         subject.notify 'great', :title => 'Guard'
       end
-    end
-
-    if linux? && libnotify_installed?
+    elsif linux? && libnotify_installed?
       it "does nothing" do
         Libnotify.should_not_receive(:show)
         subject.notify 'great', :title => 'Guard'

spec/guard_spec.rb

@@ -4,6 +4,12 @@ describe Guard do
 
   describe "Class Methods" do
     describe ".setup" do
+      before(:each) do
+        # set ENV["GUARD_NOTIFY"] to nil in case the user has ENV["GUARD_NOTIFY"] = 'false' set
+        @old_env_guard_notify = ENV["GUARD_NOTIFY"]
+        ENV["GUARD_NOTIFY"] = nil
+      end
+      after(:each) { ENV["GUARD_NOTIFY"] = @old_env_guard_notify }
       subject { ::Guard.setup }
 
       it "should retrieve itself for chaining" do
@@ -36,7 +42,7 @@ describe Guard do
       it "should turn off notifier if env[GUARD_NOTIFY] is false" do
         ::Guard::Notifier.should_receive(:turn_off)
         ENV["GUARD_NOTIFY"] = 'false'
-        ::Guard.setup(:notify => true)
+        ::Guard.setup({ :notify => true }.freeze)
         ENV["GUARD_NOTIFY"] = nil
       end
     end

spec/spec_helper.rb

@@ -15,7 +15,6 @@ RSpec.configure do |config|
   config.run_all_when_everything_filtered = true
 
   config.before(:each) do
-    Guard::Notifier.turn_off
     @fixture_path = Pathname.new(File.expand_path('../fixtures/', __FILE__))
   end