Add repository diff based subject filter

config/flay.yml

@@ -1,3 +1,3 @@
 ---
 threshold: 18
-total_score: 1173
+total_score: 1189

lib/mutant.rb

@@ -174,6 +174,7 @@ require 'mutant/reporter/cli/printer/status_progressive'
 require 'mutant/reporter/cli/printer/test_result'
 require 'mutant/reporter/cli/tput'
 require 'mutant/reporter/cli/format'
+require 'mutant/repository'
 require 'mutant/zombifier'
 
 module Mutant

lib/mutant/repository.rb

@@ -0,0 +1,66 @@
+module Mutant
+  module Repository
+    # Error raised on repository interaction problems
+    RepositoryError = Class.new(RuntimeError)
+
+    # Subject filter based on repository diff
+    class SubjectFilter
+      include Adamantium, Concord.new(:diff)
+
+      # Test if subject was touched in diff
+      #
+      # @param [Subject] subject
+      #
+      # @return [Boolean]
+      #
+      # @api private
+      def call(subject)
+        diff.touches?(subject.source_path, subject.source_lines)
+      end
+
+    end # SubjectFilter
+
+    # Diff between two objects in repository
+    class Diff
+      include Adamantium, Concord.new(:from, :to)
+
+      HEAD = 'HEAD'.freeze
+      private_constant(*constants(false))
+
+      # Create diff from head to revision
+      #
+      # @return [Diff]
+      #
+      # @api private
+      def self.from_head(to)
+        new(HEAD, to)
+      end
+
+      # Test if diff changes file at line range
+      #
+      # @param [Pathname] path
+      # @param [Range<Fixnum>] line_range
+      #
+      # @return [Boolean]
+      #
+      # @raise [RepositoryError]
+      #   when git command failed
+      #
+      # @api private
+      def touches?(path, line_range)
+        command = %W[
+          git log --pretty=oneline
+          #{from}...#{to}
+          -L #{line_range.begin},#{line_range.end}:#{path}
+        ]
+
+        stdout, status = Open3.capture2(*command, binmode: true)
+
+        fail RepositoryError, "Command #{command} failed!" unless status.success?
+
+        !stdout.empty?
+      end
+
+    end # Diff
+  end # Repository
+end # Mutant

spec/unit/mutant/repository/diff_spec.rb

@@ -0,0 +1,57 @@
+describe Mutant::Repository::Diff do
+  describe '.from_head' do
+    subject { described_class.from_head(to_revision) }
+
+    let(:to_revision) { double('to revision') }
+
+    it { should eql(described_class.new('HEAD', to_revision)) }
+  end
+
+  describe '#touches?' do
+    let(:object)        { described_class.new('from_rev', 'to_rev') }
+    let(:path)          { Pathname.new('foo.rb')                    }
+    let(:line_range)    { 1..2                                      }
+    let(:status)        { double('Status', success?: success?)      }
+    let(:stdout)        { double('Stdout', empty?: stdout_empty?)   }
+    let(:stdout_empty?) { false                                     }
+
+    subject { object.touches?(path, line_range) }
+
+    before do
+      expect(Open3).to receive(:capture2).with(
+        *expected_command,
+        binmode: true
+      ).and_return([stdout, status])
+    end
+
+    let(:expected_command) do
+      %w[
+        git log --pretty=oneline from_rev...to_rev -L 1,2:foo.rb
+      ]
+    end
+
+    context 'on failure of git command' do
+      let(:success?) { false }
+
+      it 'raises error' do
+        expect { subject }.to raise_error(Mutant::Repository::RepositoryError, "Command #{expected_command} failed!")
+      end
+    end
+
+    context 'on suuccess of git command' do
+      let(:success?) { true }
+
+      context 'on empty stdout' do
+        let(:stdout_empty?) { true }
+
+        it { should be(false) }
+      end
+
+      context 'on non empty stdout' do
+        let(:stdout_empty?) { false }
+
+        it { should be(true) }
+      end
+    end
+  end
+end

spec/unit/mutant/repository/subject_filter_spec.rb

@@ -0,0 +1,28 @@
+RSpec.describe Mutant::Repository::SubjectFilter do
+  context '#call' do
+    subject { object.call(mutant_subject) }
+
+    let(:object)       { described_class.new(diff) }
+    let(:diff)         { double('Diff')            }
+    let(:return_value) { double('Return Value')    }
+
+    let(:mutant_subject) do
+      double(
+        'Subject',
+        source_path:  double('source path'),
+        source_lines: double('source lines')
+      )
+    end
+
+    before do
+      expect(diff).to receive(:touches?).with(
+        mutant_subject.source_path,
+        mutant_subject.source_lines
+      ).and_return(return_value)
+    end
+
+    it 'connects return value to repository diff API' do
+      expect(subject).to be(return_value)
+    end
+  end
+end