Fix specification holes in Mutant::WarningFilter

lib/mutant.rb

@@ -109,15 +109,15 @@ require 'mutant/actor/receiver'
 require 'mutant/actor/sender'
 require 'mutant/actor/mailbox'
 require 'mutant/actor/env'
+require 'mutant/cache'
+require 'mutant/delegator'
+require 'mutant/isolation'
 require 'mutant/parallel'
 require 'mutant/parallel/master'
 require 'mutant/parallel/worker'
 require 'mutant/parallel/source'
-require 'mutant/cache'
-require 'mutant/delegator'
 require 'mutant/warning_filter'
 require 'mutant/require_highjack'
-require 'mutant/isolation'
 require 'mutant/mutator'
 require 'mutant/mutation'
 require 'mutant/mutator/registry'

spec/unit/mutant/warning_filter_spec.rb

@@ -88,6 +88,13 @@ RSpec.describe Mutant::WarningFilter do
       )
     end
 
+    it 'passes through non warning writes' do
+      expect($stderr).to receive(:write).with('foo')
+      object.use do
+        $stderr.write('foo')
+      end
+    end
+
     it 'resets to original stderr after execution' do
       original = $stderr
       object.use {}