Use package:stack_trace in unittest.

pkg/unittest/lib/src/utils.dart

 // Copyright (c) 2013, 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 utils;
 
 /**
  * Returns the name of the type of [x], or "Unknown" if the type name can't be
  * determined.
  */
@@ skipping 28 matching lines @@
   else if (ch == '\n')
     return '\\n';
   else if (ch == '\r')
     return '\\r';
   else if (ch == '\t')
     return '\\t';
   else
     return ch;
 }
 
+/** Indent each line in [str] by two spaces. */
+String indent(String str) =>
+  str.replaceAll(new RegExp("^", multiLine: true), "  ");
+
+/** A pair of values. */
+class Pair<E, F> {
+  E first;
+  F last;
+
+  Pair(this.first, this.last);
+
+  String toString() => '($first, $last)';
+
+  bool operator==(other) {
+    if (other is! Pair) return false;
+    return other.first == first && other.last == last;
+  }
+
+  int get hashCode => first.hashCode ^ last.hashCode;
+}
+