Replace the existing unittest APIs with the new runner infrastructure.

lib/src/prints_matcher.dart

 // Copyright (c) 2014, 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.
 
 library unittest.prints_matcher;
 
 import 'dart:async';
 
 import 'package:matcher/matcher.dart' hide completes, expect;
 
-import '../unittest.dart';
+import 'future_matchers.dart';
+import 'expect.dart';
 
 /// Matches a [Function] that prints text that matches [matcher].
 ///
 /// [matcher] may be a String or a [Matcher].
 ///
 /// If the function this runs against returns a [Future], all text printed by
 /// the function (using [Zone] scoping) until that Future completes is matched.
 ///
 /// This only tracks text printed using the [print] function.
 Matcher prints(matcher) => new _Prints(wrapMatcher(matcher));
@@ skipping 12 matching lines @@
       buffer.writeln(line);
     }));
 
     if (result is! Future) {
       var actual = buffer.toString();
       matchState['prints.actual'] = actual;
       return _matcher.matches(actual, matchState);
     }
 
     return completes.matches(result.then((_) {
-      expect(buffer.toString(), _matcher);
+      // Re-run expect() so we get the same formatting as we would without being
+      // asynchronous.
+      expect(() {
+        var actual = buffer.toString();
+        if (actual.isEmpty) return;
+
+        // Strip off the final newline because [print] will re-add it.
+        actual = actual.substring(0, actual.length - 1);
+        print(actual);
+      }, this);
     }), matchState);
   }
 
   Description describe(Description description) =>
       description.add('prints ').addDescriptionOf(_matcher);
 
   Description describeMismatch(
       item, Description description, Map matchState, bool verbose) {
     var actual = matchState.remove('prints.actual');
     if (actual == null) return description;
     if (actual.isEmpty) return description.add("printed nothing.");
 
     description.add('printed ').addDescriptionOf(actual);
 
     // Create a new description for the matcher because at least
     // [_StringEqualsMatcher] replaces the previous contents of the description.
     var innerMismatch = _matcher
         .describeMismatch(actual, new StringDescription(), matchState, verbose)
         .toString();
 
     if (innerMismatch.isNotEmpty) {
       description.add('\n   Which: ').add(innerMismatch.toString());
     }
 
     return description;
   }
 }