Improve the formatting of strings that contain unprintable ASCII characters.

test/escape_test.dart

 // Copyright (c) 2015, 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.escape_test;
 
 import 'package:matcher/src/util.dart';
 import 'package:unittest/unittest.dart';
 
 void main() {
   group('escaping should work with', () {
     _testEscaping('no escaped chars', 'Hello, world!', 'Hello, world!');
     _testEscaping('newline', '\n', r'\n');
     _testEscaping('carriage return', '\r', r'\r');
     _testEscaping('form feed', '\f', r'\f');
     _testEscaping('backspace', '\b', r'\b');
     _testEscaping('tab', '\t', r'\t');
     _testEscaping('vertical tab', '\v', r'\v');
+    _testEscaping('null byte', '\x00', r'\x00');
+    _testEscaping('ASCII control character', '\x11', r'\x11');
+    _testEscaping('delete', '\x7F', r'\x7F');
     _testEscaping('escape combos', r'\n', r'\\n');
     _testEscaping('All characters',
         'A new line\nA charriage return\rA form feed\fA backspace\b'
-        'A tab\tA vertical tab\vA slash\\',
+        'A tab\tA vertical tab\vA slash\\A null byte\x00A control char\x1D'
+        'A delete\x7F',
         r'A new line\nA charriage return\rA form feed\fA backspace\b'
-        r'A tab\tA vertical tab\vA slash\\');
+        r'A tab\tA vertical tab\vA slash\\A null byte\x00A control char\x1D'
+        r'A delete\x7F');
   });
 
   group('unequal strings remain unequal when escaped', () {
     _testUnequalStrings('with a newline', '\n', r'\n');
     _testUnequalStrings('with slash literals', '\\', r'\\');
   });
 }
 
 /// Creates a [test] with name [name] that verifies [source] escapes to value
 /// [target].
@@ skipping 14 matching lines @@
     expect(s1 != s2, isTrue, reason: 'The source values should be unequal');
 
     var escapedS1 = escape(s1);
     var escapedS2 = escape(s2);
 
     // Explicitly not using the equals matcher
     expect(escapedS1 != escapedS2, isTrue,
         reason: 'Unequal strings, when escaped, should remain unequal.');
   });
 }