revert 1204. Will investigate when I get a chance.

pkg/unittest/lib/src/expect.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.
-
-/**
- * This is the main assertion function. It asserts that [actual]
- * matches the [matcher]. [matcher] is optional and defaults to isTrue,
- * so expect can be used with a single predicate argument. [reason]
- * is optional and is typically not supplied if a reasonable matcher is
- * explicitly provided, as a reason can be generated from the matcher.
- * If [reason] is included it is appended to the reason generated
- * by the matcher.
- *
- * [matcher] can be a value in which case it will be wrapped in an
- * [equals] matcher.
- *
- * If the assertion fails, then the default behavior is to throw an
- * [ExpectException], but this behavior can be changed by calling
- * [configureExpectFailureHandler] and providing an alternative handler that
- * implements the [IFailureHandler] interface. It is also possible to
- * pass a [failureHandler] to [expect] as a final parameter for fine-
- * grained control.
- *
- * In some cases extra diagnostic info can be produced on failure (for
- * example, stack traces on mismatched exceptions). To enable these,
- * [verbose] should be specified as true;
- *
- * expect() is a 3rd generation assertion mechanism, drawing
- * inspiration from [Hamcrest] and Ladislav Thon's [dart-matchers]
- * library.
- *
- * See [Hamcrest] http://en.wikipedia.org/wiki/Hamcrest
- *     [Hamcrest] http://code.google.com/p/hamcrest/
- *     [dart-matchers] https://github.com/Ladicek/dart-matchers
- */
-void expect(actual, [matcher = isTrue, String reason = null,
-            FailureHandler failureHandler = null,
-            bool verbose = false]) {
-  matcher = wrapMatcher(matcher);
-  bool doesMatch;
-  var matchState = new MatchState();
-  try {
-    doesMatch = matcher.matches(actual, matchState);
-  } catch (e, trace) {
-    doesMatch = false;
-    if (reason == null) {
-      reason = '${(e is String) ? e : e.toString()} at $trace';
-    }
-  }
-  if (!doesMatch) {
-    if (failureHandler == null) {
-      failureHandler = getOrCreateExpectFailureHandler();
-    }
-    failureHandler.failMatch(actual, matcher, reason, matchState, verbose);
-  }
-}
-
-/**
- * Takes an argument and returns an equivalent matcher.
- * If the argument is already a matcher this does nothing,
- * else if the argument is a function, it generates a predicate
- * function matcher, else it generates an equals matcher.
- */
-Matcher wrapMatcher(x) {
-  if (x is Matcher) {
-    return x;
-  } else if (x is Function) {
-    return predicate(x);
-  } else {
-    return equals(x);
-  }
-}
-
-// The handler for failed asserts.
-FailureHandler _assertFailureHandler = null;
-
-// The default failure handler that throws ExpectExceptions.
-class DefaultFailureHandler implements FailureHandler {
-  DefaultFailureHandler() {
-    if (_assertErrorFormatter == null) {
-      _assertErrorFormatter = _defaultErrorFormatter;
-    }
-  }
-  void fail(String reason) {
-    throw new ExpectException(reason);
-  }
-  void failMatch(actual, Matcher matcher, String reason,
-      MatchState matchState, bool verbose) {
-    fail(_assertErrorFormatter(actual, matcher, reason, matchState, verbose));
-  }
-}
-
-/**
- * Changes or resets to the default the failure handler for expect()
- * [handler] is a reference to the new handler; if this is omitted
- * or null then the failure handler is reset to the default, which
- * throws [ExpectExceptions] on [expect] assertion failures.
- */
-void configureExpectFailureHandler([FailureHandler handler = null]) {
-  if (handler == null) {
-    handler = new DefaultFailureHandler();
-  }
-  _assertFailureHandler = handler;
-}
-
-FailureHandler getOrCreateExpectFailureHandler() {
-  if (_assertFailureHandler == null) {
-    configureExpectFailureHandler();
-  }
-  return _assertFailureHandler;
-}
-
-// The error message formatter for failed asserts.
-ErrorFormatter _assertErrorFormatter = null;
-
-// The default error formatter implementation.
-String _defaultErrorFormatter(actual, Matcher matcher, String reason,
-    MatchState matchState, bool verbose) {
-  var description = new StringDescription();
-  description.add('Expected: ').addDescriptionOf(matcher).
-      add('\n     but: ');
-  matcher.describeMismatch(actual, description, matchState, verbose);
-  description.add('.\n');
-  if (verbose && actual is Iterable) {
-    description.add('Actual: ').addDescriptionOf(actual).add('\n');
-  }
-  if (reason != null) {
-    description.add(reason).add('\n');
-  }
-  return description.toString();
-}
-
-/**
- * Changes or resets to default the failure message formatter for expect().
- * [formatter] is a reference to the new formatter; if this is omitted or
- * null then the failure formatter is reset to the default. The new
- * formatter is returned; this allows custom expect handlers to easily
- * get a reference to the default formatter.
- */
-ErrorFormatter configureExpectFormatter([ErrorFormatter formatter = null]) {
-  if (formatter == null) {
-    formatter = _defaultErrorFormatter;
-  }
-  return _assertErrorFormatter = formatter;
-}
-