使用Mockito对异步方法进行单元测试

原文链接 : Unit testing asynchronous methods with Mockito
译文出自 : 开发技术前线 www.devtf.cn。未经允许，不得转载!
译者 : Mr.Simple

之前我拍着胸脯承诺要维护的我博客，因此才有了这篇文章。但是请忘记我的那些承诺，我今天要写的是关于Mockito,这是一个当你写单元测试时经常会用到的对象Mock框架。

介绍

这篇文章假设你已经知道了什么是单元测试以及为什么你要写单元测试。另外，我强烈建议你阅读Martin

Fowler的这篇文章。

常见的场景

有些时候我们需要测试有回调的函数,这意味着它们是异步执行的。这些方法测试起来并不那么容易，使用

Thread.sleep(milliseconds)

来等待它们执行完成只能说是一种蹩脚的实现，并且会让你的测试具有不确定性。那么我们如何来对异步函数进行测试呢？Mockito拯救了我们！

翠花，上示例

假设我们有一个实现了

DummyCallback

接口的

DummyCaller

类，在

DummyCaller

中有一个

doSomethingAsynchronously()

函数，该函数会调用

DummyCollaborator

类的

doSomethingAsynchronously(DummyCallback
callback)

函数，在调用该函数时将这个callback参数设置为该

DummyCaller

对象。当

doSomethingAsynchronously(DummyCallback
callback)

的任务在后台线程中执行完成之后就会回调这个callback。

还是直接看代码会更容易理解 :

DummyCallback接口 :

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DummyCallback</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onSuccess</span>(List<String> result);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onFail</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> code);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

DummyCaller类 :

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DummyCaller</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DummyCallback</span> {</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 执行异步操作的代理类</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> DummyCollaborator dummyCollaborator;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 执行结果</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> List<String> result = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ArrayList<String>();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">DummyCaller</span>(DummyCollaborator dummyCollaborator) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.dummyCollaborator = dummyCollaborator;
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">doSomethingAsynchronously</span>() {
dummyCollaborator.doSomethingAsynchronously(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> List<String> <span class="hljs-title" style="box-sizing: border-box;">getResult</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.result;
}

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onSuccess</span>(List<String> result) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.result = result;
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"On success"</span>);
}

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onFail</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> code) {
System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"On Fail"</span>);
}
}
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li></ul>

真正的异步执行操作的DummyCollaborator类。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DummyCollaborator</span> {</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ERROR_CODE = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">DummyCollaborator</span>() {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// empty</span>
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">doSomethingAsynchronously</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> DummyCallback callback) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
Thread.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5000</span>);
callback.onSuccess(Collections.EMPTY_LIST);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InterruptedException e) {
callback.onFail(ERROR_CODE);
e.printStackTrace();
}
}
}).start();
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>

创建我们的测试类

我们有2种不同的选择来测试我们的异步函数，但是首先我们先创建一个DummyCollaboratorCallerTest测试类。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DummyCollaboratorCallerTest</span> {</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 要测试的类型</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> DummyCaller dummyCaller;

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Mock</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> DummyCollaborator mockDummyCollaborator;

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Captor</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> ArgumentCaptor<DummyCallback> dummyCallbackArgumentCaptor;

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Before</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">setUp</span>() {
MockitoAnnotations.initMocks(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
dummyCaller = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> DummyCaller(mockDummyCollaborator);
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

在setup函数中我们使用MockitoAnotations来初始化 Mock和ArgumentCaptor,我们暂时还不需要关心它们。

在这里我们需要关心的是在测试执行之前初始化了Mock对象和被测试的类，这些初始化代码都在setup中。记住，所有要测试的函数都要被测试两次。

让我们来看看下面的两种测试方案。

为我们的回调设置一个Anwser

这是我们使用

doAnswer()

来为一个函数进行打桩以测试异步函数的测试用例。这意味着我们需要理解返回一个回调（同步的），当被测试的方法被调用时我们生成了一个通用的anwser,这个回调会被执行。

最后，我们调用了doSomethingAsynchronously函数，并且验证了状态和交互结果。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Test</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">testDoSomethingAsynchronouslyUsingDoAnswer</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> List<String> results = Arrays.asList(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"One"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Two"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Three"</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 为callback执行一个同步anwser</span>
doAnswer(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Answer() {
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Object <span class="hljs-title" style="box-sizing: border-box;">answer</span>(InvocationOnMock invocation) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> Throwable {
((DummyCallback)invocation.getArguments()[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]).onSuccess(results);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
}
}).when(mockDummyCollaborator).doSomethingAsynchronously(
any(DummyCallback.class));

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 调用被测试的函数</span>
dummyCaller.doSomethingAsynchronously();

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 验证状态与结果</span>
verify(mockDummyCollaborator, times(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)).doSomethingAsynchronously(
any(DummyCallback.class));
assertThat(dummyCaller.getResult(), is(equalTo(results)));
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul>

[译者注 : 在doAnswer函数中当调用mockDummyCollaborator对象的doSomethingAsynchronously (final DummyCallback callback)函数时会触发Answer匿名内部类的answer(InvocationOnMock
invocation)函数]

。

使用ArgumentCaptor

第二种实现是使用ArgumentCaptor。在这里我们的callback是异步的: 我们通过ArgumentCaptor捕获传递到DummyCollaborator对象的DummyCallback回调。

最终，我们可以在测试函数级别进行所有验证，当我们想验证状态和交互结果时可以调用

onSuccess()

。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Test</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">testDoSomethingAsynchronouslyUsingArgumentCaptor</span>() {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 调用要被测试发函数</span>
dummyCaller.doSomethingAsynchronously();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> List<String> results = Arrays.asList(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"One"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Two"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Three"</span>);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Let's call the callback. ArgumentCaptor.capture() works like a matcher.</span>
verify(mockDummyCollaborator, times(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)).doSomethingAsynchronously(
dummyCallbackArgumentCaptor.capture());

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 在执行回调之前验证结果</span>
assertThat(dummyCaller.getResult().isEmpty(), is(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>));

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 调用回调的onSuccess函数</span>
dummyCallbackArgumentCaptor.getValue().onSuccess(results);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 再次验证结果</span>
assertThat(dummyCaller.getResult(), is(equalTo(results)));
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul>

结论

两种实现的主要的不同点是当使用DoAnswer()方案时我们创建了一个匿名内部类,并且将它的元素从

invocation.getArguments()

转换到我们需要的类型，但是万一我们修改了我们的参数类型，那么这个测试就会’fail
fast’。另一方面，当我们使用ArgumentCaptor时我们可能能够更精细的控制测试用例，因为我们能在测试用例中手动调用回调对象。

面对这两种方案，有时候我们不知道作何选择，但是不用担心，因为这是一个常见的问题。以我们的经验来看，同时使用这两种方案来测试异步函数会是一个更可靠的途径。

我希望这篇文章对你有用，另外，请记住，欢迎给这篇文章的反馈，或许还有更好的实现。当然，如果你有任何的疑问也可以联系我。

示例代码

代码这里。这些代码都是关于Java和Android的，因为我们在几个月前做了一场相关的演讲。

深入拓展

我强烈建议你阅读Mockito文档以对这个框架有更深入的了解，这份文档非常清晰，并且有非常棒的示例！