Add specs for mutation filter

lib/mutant.rb

@@ -103,6 +103,7 @@ require 'mutant/matcher/method/instance'
 require 'mutant/matcher/methods'
 require 'mutant/matcher/namespace'
 require 'mutant/matcher/scope'
+require 'mutant/matcher/filter'
 require 'mutant/killer'
 require 'mutant/killer/static'
 require 'mutant/killer/rspec'

spec/unit/mutant/matcher/filter_spec.rb

@@ -0,0 +1,17 @@
+require 'spec_helper'
+
+describe Mutant::Matcher::Filter do
+  let(:object)    { described_class.new(matcher, predicate) }
+  let(:matcher)   { [:foo, :bar] }
+
+  let(:predicate) { Mutant::Predicate::Attribute::Equality.new(:to_s, 'foo') }
+
+  describe '#each' do
+    subject { object.each { |item| yields << item } }
+
+    let(:yields) { []                 }
+    its(:to_a)   { should eql([:bar]) }
+
+    it_should_behave_like 'an #each method'
+  end
+end