New expectation functions plus convert old tests to use these.

lib/unittest/matcher.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.
+
+/**
+ * BaseMatcher is the base class for all matchers. To implement a new
+ * matcher, either add a class that implements from IMatcher or
+ * a class that inherits from Matcher. Inheriting from Matcher has
+ * the benefit that a default implementation of describeMismatch will
+ * be provided.
+ */
+
+class BaseMatcher implements Matcher {
+  const BaseMatcher();
+
+  /**
+   * Tests the matcher against a given [item]
+   * and return true if the match succeeds; false otherwise.
+   */
+  abstract bool matches(item);
+
+  /**
+   * Creates a textual description of a matcher,
+   * by appending to [mismatchDescription].
+   */
+  abstract Description describe(Description mismatchDescription);
+
+  /**
+   * Generates a description of the matcher failed for a particular
+   * [item], by appending the description to [mismatchDescription].
+   * It does not check whether the [item] fails the match, as it is
+   * only called after a failed match.
+   */
+  Description describeMismatch(item, Description mismatchDescription) =>
+    mismatchDescription.add('was ').addDescriptionOf(item);
+}