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// 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.
/// 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 {
int get length;
/// 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/extend the Matcher class.
/// The base Matcher class 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 {
const 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, Map 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 [Map] that was passed to and supplemented by [matches]
/// with additional information about the mismatch, and [mismatchDescription]
/// is the [Description] that is being built to describe 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,
Map matchState, bool verbose) =>