Address String#split failures by using EncodedString

Add spec for exception when failure_lines has a bad encoding

lib/rspec/core/notifications.rb

@@ -220,12 +220,19 @@ def exception_class_name
         name
       end
 
+      def exception_message
+        @exception_message ||= begin
+          string = exception.message.to_s
+          RSpec::Support::EncodedString.new(string, encoding_of(string))
+        end
+      end
+
       def failure_lines
         @failure_lines ||=
           begin
             lines = ["Failure/Error: #{read_failed_line.strip}"]
             lines << "#{exception_class_name}:" unless exception_class_name =~ /RSpec/
-            exception.message.to_s.split("\n").each do |line|
+            exception_message.split("\n").each do |line|
               lines << "  #{line}" if exception.message
             end
             lines

spec/rspec/core/encoding_spec.rb

@@ -0,0 +1,49 @@
+# encoding: utf-8
+require 'spec_helper'
+require 'rspec/core/notifications'
+
+RSpec.describe "FailedExampleNotification", :if => String.method_defined?(:encoding) do
+  include FormatterSupport
+
+  let(:notification) { ::RSpec::Core::Notifications::FailedExampleNotification.new(example) }
+
+  before do
+    example.metadata[:absolute_file_path] = __FILE__
+  end
+
+  describe '#message_lines' do
+    let(:message_with_invalid_byte_sequence) do
+      "\xEF \255 \xAD I have bad bytes".force_encoding(Encoding::UTF_8)
+    end
+    let(:expected_message) { "? ? ? I have bad bytes" }
+    let(:exception) do
+      instance_double(
+        Exception,
+        :backtrace => [ "#{__FILE__}:#{__LINE__}"],
+        :message => message_with_invalid_byte_sequence
+      )
+    end
+
+    let(:example_group) do
+      class_double(
+        RSpec::Core::ExampleGroup,
+        :metadata => {},
+        :parent_groups => [],
+        :location => "#{__FILE__}:#{__LINE__}"
+      )
+    end
+
+    before do
+      allow(example).to receive(:example_group) { example_group }
+    end
+
+    context "when failure_lines contains an invalid byte sequence" do
+      it "replaces bad bytes with a '?'" do
+        lines = notification.message_lines
+        expect(lines[0]).to match %r{\AFailure\/Error}
+        expect(lines[1].strip).to eq(expected_message)
+      end
+    end
+
+  end
+end