Correctly match and print strings with escaped values

lib/src/core_matchers.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library matcher.core_matchers;
 
 import 'description.dart';
+import 'escape.dart';
 import 'interfaces.dart';
 import 'util.dart';
 
 /// Returns a matcher that matches the isEmpty property.
 const Matcher isEmpty = const _Empty();
 
 class _Empty extends Matcher {
   const _Empty();
 
   bool matches(item, Map matchState) => item.isEmpty;
@@ skipping 272 matching lines @@
   Description describe(Description description) =>
       description.addDescriptionOf(_value);
 
   Description describeMismatch(
       item, Description mismatchDescription, Map matchState, bool verbose) {
     if (item is! String) {
       return mismatchDescription.addDescriptionOf(item).add('is not a string');
     } else {
       var buff = new StringBuffer();
       buff.write('is different.');
-      var escapedItem = _escape(item);
-      var escapedValue = _escape(_value);
+      var escapedItem = escape(item);
+      var escapedValue = escape(_value);
       int minLength = escapedItem.length < escapedValue.length
           ? escapedItem.length
           : escapedValue.length;
       int start;
       for (start = 0; start < minLength; start++) {
         if (escapedValue.codeUnitAt(start) != escapedItem.codeUnitAt(start)) {
           break;
         }
       }
       if (start == minLength) {
@@ skipping 15 matching lines @@
         _writeTrailing(buff, escapedItem, start);
         buff.write('\n          ');
         for (int i = (start > 10 ? 14 : start); i > 0; i--) buff.write(' ');
         buff.write('^\n Differ at offset $start');
       }
 
       return mismatchDescription.replace(buff.toString());
     }
   }
 
-  static String _escape(String s) =>
-      s.replaceAll('\n', '\\n').replaceAll('\r', '\\r').replaceAll('\t', '\\t');
-
   static void _writeLeading(StringBuffer buff, String s, int start) {
     if (start > 10) {
       buff.write('... ');
       buff.write(s.substring(start - 10, start));
     } else {
       buff.write(s.substring(0, start));
     }
   }
 
   static void _writeTrailing(StringBuffer buff, String s, int start) {
@@ skipping 297 matching lines @@
         .addDescriptionOf(matchState['feature']);
     var innerDescription = new StringDescription();
     _matcher.describeMismatch(
         matchState['feature'], innerDescription, matchState['state'], verbose);
     if (innerDescription.length > 0) {
       mismatchDescription.add(' which ').add(innerDescription.toString());
     }
     return mismatchDescription;
   }
 }