Add expectAsyncX and expectAsyncUntilX methods, and deprecate the old methods.

test/util/one_off_handler_test.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:async';
 
 import 'package:shelf/shelf.dart' as shelf;
 import 'package:test/src/util/one_off_handler.dart';
 import 'package:test/test.dart';
 
 void main() {
   var handler;
   setUp(() => handler = new OneOffHandler());
 
   _handle(request) => new Future.sync(() => handler.handler(request));
 
   test("returns a 404 for a root URL", () async {
     var request = new shelf.Request("GET", Uri.parse("http://localhost/"));
     expect((await _handle(request)).statusCode, equals(404));
   });
 
   test("returns a 404 for an unhandled URL", () async {
     var request = new shelf.Request("GET", Uri.parse("http://localhost/1"));
     expect((await _handle(request)).statusCode, equals(404));
   });
 
   test("passes a request to a handler only once", () async {
-    var path = handler.create(expectAsync((request) {
+    var path = handler.create(expectAsync1((request) {
       expect(request.method, equals("GET"));
       return new shelf.Response.ok("good job!");
     }));
 
     var request = new shelf.Request("GET", Uri.parse("http://localhost/$path"));
     var response = await _handle(request);
     expect(response.statusCode, equals(200));
     expect(response.readAsString(), completion(equals("good job!")));
 
     request = new shelf.Request("GET", Uri.parse("http://localhost/$path"));
     expect((await _handle(request)).statusCode, equals(404));
   });
 
   test("passes requests to the correct handlers", () async {
-    var path1 = handler.create(expectAsync((request) {
+    var path1 = handler.create(expectAsync1((request) {
       expect(request.method, equals("GET"));
       return new shelf.Response.ok("one");
     }));
 
-    var path2 = handler.create(expectAsync((request) {
+    var path2 = handler.create(expectAsync1((request) {
       expect(request.method, equals("GET"));
       return new shelf.Response.ok("two");
     }));
 
-    var path3 = handler.create(expectAsync((request) {
+    var path3 = handler.create(expectAsync1((request) {
       expect(request.method, equals("GET"));
       return new shelf.Response.ok("three");
     }));
 
     var request = new shelf.Request(
         "GET", Uri.parse("http://localhost/$path2"));
     var response = await _handle(request);
     expect(response.statusCode, equals(200));
     expect(response.readAsString(), completion(equals("two")));
 
     request = new shelf.Request("GET", Uri.parse("http://localhost/$path1"));
     response = await _handle(request);
     expect(response.statusCode, equals(200));
     expect(response.readAsString(), completion(equals("one")));
 
     request = new shelf.Request("GET", Uri.parse("http://localhost/$path3"));
     response = await _handle(request);
     expect(response.statusCode, equals(200));
     expect(response.readAsString(), completion(equals("three")));
   });
 }