pkg/(unit)test: include a copy of old matcher

lib/src/matcher/description.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.description;
+
+import 'interfaces.dart';
+import 'pretty_print.dart';
+
+/// The default implementation of [Description]. This should rarely need
+/// substitution, although conceivably it is a place where other languages
+/// could be supported.
+class StringDescription implements Description {
+  final StringBuffer _out = new StringBuffer();
+
+  /// Initialize the description with initial contents [init].
+  StringDescription([String init = '']) {
+    _out.write(init);
+  }
+
+  int get length => _out.length;
+
+  /// Get the description as a string.
+  String toString() => _out.toString();
+
+  /// Append [text] to the description.
+  Description add(String text) {
+    _out.write(text);
+    return this;
+  }
+
+  /// Change the value of the description.
+  Description replace(String text) {
+    _out.clear();
+    return add(text);
+  }
+
+  /// Appends a description of [value]. If it is an IMatcher use its
+  /// describe method; if it is a string use its literal value after
+  /// escaping any embedded control characters; otherwise use its
+  /// toString() value and wrap it in angular "quotes".
+  Description addDescriptionOf(value) {
+    if (value is Matcher) {
+      value.describe(this);
+    } else {
+      add(prettyPrint(value, maxLineLength: 80, maxItems: 25));
+    }
+    return this;
+  }
+
+  /// Append an [Iterable] [list] of objects to the description, using the
+  /// specified [separator] and framing the list with [start]
+  /// and [end].
+  Description addAll(
+      String start, String separator, String end, Iterable list) {
+    var separate = false;
+    add(start);
+    for (var item in list) {
+      if (separate) {
+        add(separator);
+      }
+      addDescriptionOf(item);
+      separate = true;
+    }
+    add(end);
+    return this;
+  }
+}