Add Mutant::Matcher.{parse,from_string}

These are used in CLI to create maters from strings

lib/mutant/matcher.rb

@@ -1,7 +1,8 @@
 module Mutant
   # Abstract matcher to find ASTs to mutate
   class Matcher
-    include Enumerable, Abstract
+    include Enumerable, Abstract, Immutable
+    extend DescendantsTracker
 
     # Enumerate subjects
     #
@@ -19,7 +20,36 @@ module Mutant
     #
     abstract_method :identification
 
-  private
+    # Return matcher
+    #
+    # @param [String] input
+    #
+    # @return [nil]
+    #   returns nil as default implementation
+    #
+    # @api private
+    #
+    def self.parse(input)
+      nil
+    end
 
+    # Return match from string
+    #
+    # @param [String] input
+    #
+    # @return [Matcher]
+    #   returns matcher input if successful
+    #
+    # @return [nil]
+    #   returns nil otherwise
+    #
+    def self.from_string(input)
+      descendants.each do |descendant|
+        matcher = descendant.parse(input)
+        return matcher if matcher
+      end
+
+      nil
+    end
   end
 end

spec/unit/mutant/matcher/class_methods/from_string_spec.rb

@@ -0,0 +1,49 @@
+require 'spec_helper'
+
+describe Mutant::Matcher, '.from_string' do
+  subject { object.from_string(input) }
+
+  let(:input)   { mock('Input')   }
+  let(:matcher) { mock('Matcher') }
+
+  let(:descendant_a) { mock('Descendant A', :parse => nil) }
+  let(:descendant_b) { mock('Descendant B', :parse => nil) }
+
+  let(:object) { described_class }
+
+  before do
+    described_class.stub(:descendants => [descendant_a, descendant_b])
+  end
+
+  context 'when no descendant takes the input' do
+    it { should be(nil) }
+
+    it_should_behave_like 'an idempotent method'
+  end
+
+  context 'when one descendant handles input' do
+    before do
+      descendant_a.stub(:parse => matcher)
+    end
+
+    it { should be(matcher) }
+
+    it_should_behave_like 'an idempotent method'
+  end
+
+  pending 'when more than one descendant handles input' do
+    let(:matcher_b) { mock('Matcher B') }
+
+    before do
+      descendant_a.stub(:parse => matcher)
+      descendant_b.stub(:parse => matcher_b)
+    end
+
+    it 'should return the first matcher' do 
+      should be(matcher)
+    end
+
+    it_should_behave_like 'an idempotent method'
+  end
+end
+

spec/unit/mutant/matcher/class_methods/parse_spec.rb

@@ -0,0 +1,12 @@
+require 'spec_helper'
+
+describe Mutant::Matcher, '.parse' do
+  subject { object.parse(input) }
+
+  let(:input) { mock('Input') }
+  let(:object) { described_class }
+
+  it { should be(nil) }
+
+  it_should_behave_like 'an idempotent method'
+end

spec/unit/mutant/matcher/method/classifier/class_methods/run_spec.rb

@@ -21,8 +21,8 @@ describe Mutant::Matcher::Method::Classifier, '.run' do
   context 'with invalid notation' do
     let(:input) { 'Foo' }
 
-    it 'should raise error' do
-      expect { subject }.to raise_error(ArgumentError, "Cannot determine subject from #{input.inspect}")
+    it 'should return nil' do
+      should be(nil)
     end
   end
 end