Correctly implement and specify singleton method extraction

lib/mutant/matcher/method/singleton.rb

@@ -28,8 +28,15 @@ module Mutant
         # @api private
         #
         def self.singleton_methods(scope)
-          scope.singleton_class.instance_methods(false).reject do |method|
-            method.to_sym == :__class_init__
+          singleton_class = scope.singleton_class
+
+          names = 
+            singleton_class.public_instance_methods(false)   +
+            singleton_class.private_instance_methods(false)  +
+            singleton_class.protected_instance_methods(false)
+
+          names.map(&:to_sym).sort.reject do |name|
+            name.to_sym == :__class_init__
           end
         end
 

spec/unit/mutant/matcher/method/singleton/class_methods/each_spec.rb

@@ -0,0 +1,45 @@
+require 'spec_helper'
+
+describe Mutant::Matcher::Method::Singleton, '.each' do
+  subject { object.each(scope) { |item| yields << item } }
+
+  let(:each_arguments) { [scope] }
+
+  let(:object)   { described_class }
+  let(:yields)   { []              }
+
+  context 'when scope is a Class' do
+    let(:scope) do
+      ancestor = Class.new do
+        def self.ancestor_method
+        end
+
+        def self.name; 'SomeRandomClass'; end
+      end
+
+      Class.new(ancestor) do
+        def self.public_method; end
+        public_class_method :public_method
+
+        class << self
+          def protected_method; end
+
+          protected :protected_method
+        end
+
+        def self.private_method; end
+        private_class_method :private_method
+      end
+    end
+
+    it 'should yield instance method matchers' do
+      expected = [
+        Mutant::Matcher::Method::Singleton.new(scope, :public_method   ),
+        Mutant::Matcher::Method::Singleton.new(scope, :protected_method),
+        Mutant::Matcher::Method::Singleton.new(scope, :private_method  )
+      ].sort_by(&:method_name)
+
+      expect { subject }.to change { yields.dup }.from([]).to(expected)
+    end
+  end
+end