Merge pull request #74 from jessekempf/dump_rspec_stderr_when_noop_mutant_is_not_killed

Surface the output of rspec failures when killing noop mutants.

lib/mutant/killer/rspec.rb

@@ -18,9 +18,21 @@ module Mutant
       def run
         mutation.insert
         # TODO: replace with real streams from configuration
+        # Note: we assume the only interesting output from a failed rspec run is stderr.
         require 'stringio'
-        null = StringIO.new
-        !::RSpec::Core::Runner.run(command_line_arguments, null, null).zero?
+        rspec_err = StringIO.new
+
+        killed = !::RSpec::Core::Runner.run(command_line_arguments, nil, rspec_err).zero?
+
+        if killed and mutation.should_survive?
+          rspec_err.rewind
+
+          puts "#{mutation.class} test failed."
+          puts 'RSpec stderr:'
+          puts rspec_err.read
+        end
+
+        killed
       end
 
       # Return command line arguments

lib/mutant/mutation.rb

@@ -28,6 +28,18 @@ module Mutant
     #
     abstract_method :success?
 
+    # Indicate if a killer should treat a kill as problematic
+    #
+    # @return [true]
+    #   if killing is unexpected
+    #
+    # @return [false]
+    #   if killing is expected
+    #
+    # @api private
+    #
+    abstract_method :should_survive?
+
     # Insert mutated node
     #
     # FIXME:

lib/mutant/mutation/evil.rb

@@ -30,6 +30,16 @@ module Mutant
         killer.killed?
       end
 
+      # Indicate if a killer should treat a kill as problematic.
+      #
+      # @return [false] Killing evil mutants is not problematic.
+      #
+      # @api private
+      #
+      def should_survive?
+        false
+      end
+
     end # Evil
   end # Mutation
 end # Mutant

lib/mutant/mutation/neutral.rb

@@ -10,6 +10,19 @@ module Mutant
 
         SYMBOL = 'noop'
 
+        # Indicate if a killer should treat a kill as problematic.
+        #
+        # @return [false] Killing noop mutants is a serious problem. Failures
+        #   in noop may indicate a broken test suite, but they can also be an
+        #   indication  mutant has altered the runtime environment in a subtle
+        #   way and tickled an odd bug.
+        #
+        # @api private
+        #
+        def should_survive?
+          false
+        end
+
       end
 
       # Return identification
@@ -39,6 +52,16 @@ module Mutant
         !killer.killed?
       end
 
+      # Indicate if a killer should treat a kill as problematic.
+      #
+      # @return [true] Neutral mutants must die.
+      #
+      # @api private
+      #
+      def should_survive?
+        false
+      end
+
     end # Neutral
   end # Mutation
 end # Mutant

spec/unit/mutant/killer/rspec/class_methods/new_spec.rb

@@ -6,7 +6,7 @@ describe Mutant::Killer::Rspec, '.new' do
 
   let(:strategy)         { double('Strategy', :spec_files => ['foo'], :error_stream => $stderr, :output_stream => $stdout) }
   let(:context)          { double('Context')                                                                               }
-  let(:mutation)         { double('Mutation', :subject => mutation_subject)                                                }
+  let(:mutation)         { double('Mutation', :subject => mutation_subject, :should_survive? => false)                     }
   let(:mutation_subject) { double('Mutation Subject')                                                                      }
 
   let(:object)  { described_class }