mock框架搞什么搞？

今天早上一时兴起，去网上下载下来JMock，EasyMock最新版本来玩玩。用来测试的行为很简单。就是有一个窗体，上面有一个文本框，一个按钮。如果点击按钮，就会把文本框的内容设置为“Hello”。应用MVP模式，这个行为应该在Presenter中，而View接口应该是这样的：

public interface View {
	public void setText(String text);
	public void addActionListener(ActionListener actionListener);
}

我这里就不TDD了，直接给出Presenter的实现，然后我们来看JMock和EasyMock如何处理这个问题。

public class Presenter {
	public Presenter(final View view) {
		view.addActionListener(new ActionListener() {
			public void actionPerformed() {
				view.setText("Hello");
			}
		});
	}
}

好的，我先来写一段伪测试代码：

引用

创建MockView
创建Presenter，传以MockView做为参数
在MockView上触发事件
验证MockView的SetText方法被调用了

然后就用JMock来实现这段伪代码。

@Test
public void test_click_button_should_set_text_hello() {
		Mockery mockery = new Mockery();
		final View mockView = mockery.mock(View.class);
		final ActionListenerMatcher actionListenerMatcher = new ActionListenerMatcher();
		mockery.checking(new Expectations() {
			{
				one(mockView).addActionListener(
						with(actionListenerMatcher));
				one(mockView).setText("Hello");
			}
		});
		new Presenter(mockView);
		actionListenerMatcher.fireActionPerformed();
		mockery.assertIsSatisfied();
	}

由于JMock没有对触发事件提供直接的支持，所以是自己写了一个ActionListenerMatcher来达到这个目的的。这个Matcher的实现如下：

public class ActionListenerMatcher extends BaseMatcher<ActionListener> {

	private ActionListener actionListener;

	public boolean matches(Object item) {
		actionListener = (ActionListener) item;
		return true;
	}

	public void fireActionPerformed() {
		actionListener.actionPerformed();
	}

	public void describeTo(Description description) {
	}

}

可以看到之所以要这个Matcher是因为，我们需要有一个地方来保存Presenter传进来的listener，并且提供一个用来触发事件的方法。

EasyMock的实现与之非常类似，此处不再赘述。代码可以参见附件。

我们可以看到什么？我看到的是，测试时候的Intention（意图）完全掩盖在冗长复杂的代码之中了。如果不用Mock该怎么做？很简单：

@Test
public void test_click_button_should_set_text_hello() {
		MockView mockView = new MockView();
		new Presenter(mockView);
		mockView.fireActionPerformed();
		Assert.assertEquals("Hello", mockView.getText());
	}

这段代码是不是和上面的伪代码一模一样？MockView是这样的：

private class MockView implements View {
		private ActionListener actionListener;
		private String text;
		public void addActionListener(ActionListener actionListener) {
			this.actionListener = actionListener;
		}
		public void setText(String text) {
			this.text = text;
		}
		public String getText() {
			return text;
		}
		public void fireActionPerformed() {
			actionListener.actionPerformed();
		}
	}

做完这个实验，我不得不说。Mock框架，搞什么搞！简单一点不好么？

评论

3 楼 raimundox 2007-05-11  

你给的例子不是Mock，至多是Fake。各种区别见马大叔的Mocks Aren't Stubs：

* Dummy objects are passed around but never actually used. Usually they are just used to fill parameter lists.
* Fake objects actually have working implementations, but usually take some shortcut which makes them not suitable for production (an in memory database is a good example).
* Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what's programmed in for the test. Stubs may also record information about calls, such as an email gateway stub that remembers the messages it 'sent', or maybe only how many messages it 'sent'.
* Mocks are what we are talking about here: objects pre-programmed with expectations which form a specification of the calls they are expected to receive.

因此实际上，不是JMock或EasyMock框架复杂，而是你给的例子中，Mock不是最佳选择，如果View里东西再多一点，Fake可能就不太合适了。

2 楼 taowen 2007-05-11  

简单问题是怎么被mock框架搞复杂的，这个例子难道还不明白吗？静态构造函数，泛型。构造出奇技淫巧的语法。结果缺并没有把事情搞简单。这还不能够说明问题？

1 楼 dustinth 2007-05-11  

搞明白哪些地方可以使用Mock先再骂娘, OK?