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copied!<p>Full example of how to test with the <code>completion</code> matcher is as follows.</p> <pre class="lang-java prettyprint-override"><code>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}))); }); } </code></pre> <p>The unit test runner might not complete before this code completes. So it would seem that the unit test executed correctly. With <code>Future</code>s that might take longer periods of time to complete the proper way is to utilize <code>completion</code> matcher available in unittest package. </p> <pre class="lang-java prettyprint-override"><code>/** * 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)); </code></pre> <p>One would be tempted to do the following which would be incorrect way of unit testing a returned Future in dart. WARNING: below is an incorrect way to test Futures. </p> <pre class="lang-java prettyprint-override"><code>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"]); }); }); } </code></pre>

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