revert 1204. Will investigate when I get a chance.

pkg/unittest/lib/src/interfaces.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.
-
-// To decouple the reporting of errors, and allow for extensibility of
-// matchers, we make use of some interfaces.
-
-/**
- * The ErrorFormatter type is used for functions that
- * can be used to build up error reports upon [expect] failures.
- * There is one built-in implementation ([defaultErrorFormatter])
- * which is used by the default failure handler. If the failure handler
- * is replaced it may be desirable to replace the [stringDescription]
- * error formatter with another.
- */
-typedef String ErrorFormatter(actual, Matcher matcher, String reason,
-    MatchState matchState, bool verbose);
-
-/**
- * Matchers build up their error messages by appending to
- * Description objects. This interface is implemented by
- * StringDescription. This interface is unlikely to need
- * other implementations, but could be useful to replace in
- * some cases - e.g. language conversion.
- */
-abstract class Description {
-  /** Change the value of the description. */
-  Description replace(String text);
-
-  /** This is used to add arbitrary text to the description. */
-  Description add(String text);
-
-  /** This is used to add a meaningful description of a value. */
-  Description addDescriptionOf(value);
-
-  /**
-   * This is used to add a description of an [Iterable] [list],
-   * with appropriate [start] and [end] markers and inter-element [separator].
-   */
-  Description addAll(String start, String separator, String end,
-                     Iterable list);
-}
-
-/**
- * [expect] Matchers must implement the Matcher class.
- * The base Matcher class that implements this interface has
- * a generic implementation of [describeMismatch] so this does
- * not need to be provided unless a more clear description is
- * required. The other two methods ([matches] and [describe])
- * must always be provided as they are highly matcher-specific.
- */
-abstract class Matcher {
-  /**
-   * This does the matching of the actual vs expected values.
-   * [item] is the actual value. [matchState] can be supplied
-   * and may be used to add details about the mismatch that are too
-   * costly to determine in [describeMismatch].
-   */
-  bool matches(item, MatchState matchState);
-
-  /** This builds a textual description of the matcher. */
-  Description describe(Description description);
-
-  /**
-   * This builds a textual description of a specific mismatch. [item]
-   * is the value that was tested by [matches]; [matchState] is
-   * the [MatchState] that was passed to and supplemented by [matches]
-   * with additional information about the mismact, and [mismatchDescription]
-   * is the [Description] that is being built to decribe the mismatch.
-   * A few matchers make use of the [verbose] flag to provide detailed
-   * information that is not typically included but can be of help in
-   * diagnosing failures, such as stack traces.
-   */
-  Description describeMismatch(item, Description mismatchDescription,
-      MatchState matchState, bool verbose);
-}
-
-/**
- * Failed matches are reported using a default IFailureHandler.
- * The default implementation simply throws ExpectExceptions;
- * this can be replaced by some other implementation of
- * IFailureHandler by calling configureExpectHandler.
- */
-abstract class FailureHandler {
-  /** This handles failures given a textual decription */
-  void fail(String reason);
-
-  /**
-   * This handles failures given the actual [value], the [matcher]
-   * the [reason] (argument from [expect]), some additonal [matchState]
-   * generated by the [matcher], and a verbose flag which controls in
-   * some cases how much [matchState] information is used. It will use
-   * these to create a detailed error message (typically by calling
-   * an [ErrorFormatter]) and then call [fail] with this message.
-   */
-  void failMatch(actual, Matcher matcher, String reason,
-                 MatchState matchState, bool verbose);
-}
-