Expand writer methods correctly to spec files

lib/mutant/strategy/rspec/example_lookup.rb

@@ -65,7 +65,7 @@ module Mutant
         def spec_file
           matcher.method_name.to_s.
             gsub(/\?\z/, '_predicate').
-            gsub(/\=\z/, '_writer').
+            gsub(/=\z/, '_writer').
             gsub(/!\z/, '_bang') + '_spec.rb'
         end
         memoize :spec_file

spec/unit/mutant/strategy/rspec/example_lookup/spec_file_spec.rb

@@ -0,0 +1,46 @@
+require 'spec_helper'
+
+describe Mutant::Strategy::Rspec::ExampleLookup, '#spec_file' do
+
+  let(:object)           { described_class.new(mutation)                  }
+  let(:mutation)         { mock('Mutation', :subject => mutation_subject) }
+  let(:mutation_subject) { mock('Subject', :matcher => matcher)           }
+  let(:matcher)          { mock('Matcher', :method_name => method_name)   }
+
+  subject { object.send(:spec_file) }
+
+  shared_examples_for 'Mutant::Strategy::Rspec::ExampleLookup#spec_file' do
+    it_should_behave_like 'an idempotent method'
+
+    it { should eql(expected_spec_file) }
+    it { should be_frozen }
+  end
+
+  context 'with writer method' do
+    let(:method_name) { 'foo=' }
+    let(:expected_spec_file) { 'foo_writer_spec.rb' }
+
+    it_should_behave_like 'Mutant::Strategy::Rspec::ExampleLookup#spec_file'
+  end
+
+  context 'with bang method' do
+    let(:method_name) { 'foo!' }
+    let(:expected_spec_file) { 'foo_bang_spec.rb' }
+
+    it_should_behave_like 'Mutant::Strategy::Rspec::ExampleLookup#spec_file'
+  end
+
+  context 'with predicate method' do
+    let(:method_name) { 'foo?' }
+    let(:expected_spec_file) { 'foo_predicate_spec.rb' }
+
+    it_should_behave_like 'Mutant::Strategy::Rspec::ExampleLookup#spec_file'
+  end
+
+  context 'with regular method' do
+    let(:method_name) { 'foo' }
+    let(:expected_spec_file) { 'foo_spec.rb' }
+
+    it_should_behave_like 'Mutant::Strategy::Rspec::ExampleLookup#spec_file'
+  end
+end