Testing 强制流事件交付

我试图在我的服务中测试流事件，但遇到了一个问题：有没有办法在异步流中同步传递事件？以下是简化的代码示例：

test("deliver event", () {
  StreamController sc = new StreamController();
  String v = "old";
  sc.stream.listen((val) {v = val;});
  sc.add("new");
  expect(v, "new"); // test fails: actual value is "old"
});

---

从异步到同步，您无法进行任何操作

import 'dart:async';
Future main() async {
  StreamController sc = new StreamController();
  String v = "old";
  var subscr = sc.stream.listen((val) { v = val;});
  sc.add("new");
  subscr.asFuture().then((_) {
    print('assert v == "new": ${v == 'new'}'); 
    // expect(v, "new"); // test fails: actual value is "old"
  });
  sc.close();
}

---

我更新了我的答案。