Add some basic interfaces that will be used for the test runner.

lib/src/suite.dart

Index: lib/src/suite.dart
diff --git a/lib/src/suite.dart b/lib/src/suite.dart
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+++ b/lib/src/suite.dart
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+// 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 unittest.suite;
+
+import 'dart:collection';
+
+import 'test.dart';
+
+/// A test suite.
+///
+/// A test suite is a set of tests that are intended to be run together and that
+/// share default configuration.
+class Suite {
+  /// The name of the test suite.
+  final String name;
+
+  /// The tests in the test suite.
+  final List<Test> tests;
+
+  Suite(this.name, Iterable<Test> tests)
+      : tests = new UnmodifiableListView<Test>(tests.toList());
+}