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.

abstract class BaseMatcher implements Matcher {
  const BaseMatcher();

  /**
   * Tests the matcher against a given [item]
   * and return true if the match succeeds; false otherwise.
   * [matchState] may be used to return additional info for
   * the use of [describeMismatch].
   */
  abstract bool matches(item, MatchState matchState);

  /**
   * 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. There may be additional info
   * about the mismatch in [matchState].
   */
  Description describeMismatch(item, Description mismatchDescription,
                               MatchState matchState, bool verbose) =>
    mismatchDescription.add('was ').addDescriptionOf(item);
}