unit-testing - 我应该如何在 Dart 中测试 Future？

Question

如何测试返回 Future 的方法在测试运行器完成之前？我有一个问题，我的单元测试运行程序在异步方法完成之前完成。

Answer 1

如何使用 completion 进行测试的完整示例匹配器如下。

import 'package:unittest/unittest.dart';

class Compute {
  Future<Map> sumIt(List<int> data) {
    Completer completer = new Completer();
    int sum = 0;
    data.forEach((i) => sum += i);
    completer.complete({"value" : sum});
    return completer.future;
  }
}

void main() {
  test("testing a future", () {
    Compute compute = new Compute();    
    Future<Map> future = compute.sumIt([1, 2, 3]);
    expect(future, completion(equals({"value" : 6})));
  });
}

在此代码完成之前，单元测试运行程序可能无法完成。因此，单元测试似乎正确执行。与 Future可能需要更长时间才能完成正确方法的 s 是利用 completion匹配器在 unittest 包中可用。

/**
 * Matches a [Future] that completes succesfully with a value that matches
 * [matcher]. Note that this creates an asynchronous expectation. The call to
 * `expect()` that includes this will return immediately and execution will
 * continue. Later, when the future completes, the actual expectation will run.
 *
 * To test that a Future completes with an exception, you can use [throws] and
 * [throwsA].
 */
Matcher completion(matcher) => new _Completes(wrapMatcher(matcher));

人们可能会尝试执行以下操作，这将是在 dart 中对返回的 Future 进行单元测试的不正确方式。警告:下面是测试 future 的不正确方法。

import 'package:unittest/unittest.dart';

class Compute {
  Future<Map> sumIt(List<int> data) {
    Completer completer = new Completer();
    int sum = 0;
    data.forEach((i) => sum+=i);
    completer.complete({"value":sum});
    return completer.future;
  }
}

void main() {
  test("testing a future", () {
    Compute compute = new Compute();
    compute.sumIt([1, 2, 3]).then((Map m) {
      Expect.equals(true, m.containsKey("value"));
      Expect.equals(6, m["value"]);
    });
  });
}