��试驱动开发案例之自动售货机（�W?集）

Baoquan Inside — Sat, 25 Feb 2006 15:12:00 GMT

��试驱动开�?TDD, Test Driven Development)是一�U�很有意思的软�g开发方式，本集以较��的步伐体验TDD�?BR>
/** A program simulation of an automat.

* Director: Zuo Baoquan

* Contact me:

* Blog: http://www.tkk7.com/BaoquanInside
* MSN: Baoquan.Zuo [at] hotmail.com

* Email: Baoquan.Zuo [at] gmail.com

引言�Q?/DIV>

�Q�该问题截取自�?A >面向对象的设计与模式�?Written by Cay Horstmann) Exercise 2.18

设计�q�实��C��个模拟自动售货机的程序。通过�l�机器投入正��的��币�Q�便可以购买到相应的商品。用户从一个可用的商品列表中选择商品、投入硬币�ƈ得到商品。如果没有��够的钱币或由于此商品已销售完毕，则将��币退回。操作员可以重新�?STRONG>�?/STRONG>�q�将钱币取走�?/DIV>

场景#1

地点�Q�同��大学西南楼

涉众�Q�我�Q�空自动售货�?/DIV>

寝室楼里面刚搬来了一台空的自动售货机�Q�那我们来测试一下：

public class TestEmptyAutomat extends TestCase
{
public void testIsEmpty()
{
Automat automat = new Automat();

assertTrue("it should be empty.", automat.isEmpty());
}
}

Eclipse提示"Automat cannot be resolved to a type"�Q�好�Q�看我的�Q?/DIV>

public class Automat
{
public Automat() // constructor stub
{
}
}

再露一手：

//class Automat

public boolean isEmpty()

{

return true;

}

全部保存�Q�运行测试，呵呵�Q�绿色进度条�Q�测试成功！

好，既然我们�q�没有投�q�硬币，那么余额应该�?了～

// class TestEmptyAutomat

public void testBalance()
{
Automat automat = new Automat();
assertEquals("the balance should be 0.", 0, automat.balance);
}

�l�箋使用我们的法宝：

// class Automat

public final int balance = 0;

�q�行��试�Q�yeah!

看了一遍测试程序，军_��优化一下：

public class TestEmptyAutomat extends TestCase
{
protected void setUp() throws Exception
{
    super.setUp();
    automat = new Automat();
  }

public void testIsEmpty()
{
    assertTrue("it should be empty.", automat.isEmpty());
  }

public void testBalance()
{
    assertEquals("the balance should be 0.", 0, automat.balance);
}

private Automat automat;
}

再运行一�ơ测试，呵呵�Q�又是绿�Ԍ��

场景#2

地点�Q�同��大学西南楼

涉众�Q�我�Q�自动售货机(有一瓶百事可�?

好消息，楼长在自动售货机里面放了一瓶Pepsi�?/DIV>

public class TestAutomatWithOnePepsi extends TestCase
{
  protected void setUp() throws Exception
{
    super.setUp();
   automat = new Automat();

pepsi = new Pepsi(); // 一瓶百事可�?/DIV>

automat.add(pepsi); // 楼长阿姨攄��?BR> }

public void testEmpty()
{
assertFalse("it should not be empty.", automat.isEmpty());
}

public Automat automat;

public Pepsi pepsi;
}

接着创徏Pepsi�c?/DIV>

public class Pepsi
{
public Pepsi() // constructor stub
{

}
}

再给Automat��d��add�Ҏ��Q?/DIV>

// class Automat

public void add(Pepsi pepsi)

{

}

好，现在有两个TC(Test Case)了，��Z��q�行两个��试案例�Q�我们来创徏一个Test Suite:

public class AutomatTests
{
public static Test suite()
{
    TestSuite suite = new TestSuite("Test for net.mybec.automat");
    //$JUnit-BEGIN$
    suite.addTestSuite(TestAutomatWithOnePepsi.class);
    suite.addTestSuite(TestEmptyAutomat.class);
    //$JUnit-END$

return suite;
}
}

�~�译成功�Q�运行AutomatTests�Q�红色进度条。TestEmptyAutomat�l�色�Q�TestAutomatWithOnePepsi�U�色。呵呵，看来要让add做点事情了�?/DIV>

// class Automat

public void add(Pepsi pepsi)

{

goods.add(pepsi);

}

// ��d��一个装Pepsi的数�l�列�?/DIV>

private final ArrayList goods = new ArrayList();

// 修改isEmpty�Ҏ��

public boolean isEmpty()
{
return goods.isEmpty();
}

再次�q�行AutomatTests�Q�呵呵，�l�色�Q�我们喜�Ƣ！

好，我们再看看Automat的余额：

// class TestAutomatWithOnePepsi

public void testBalance()
{
assertEquals("the balance should be 0.", 0, automat.balance);
}

�q�行一遍测试，Ok�?/DIV>

我们�q�没有投��币�Q�当然不能买百事可乐了：

// class TestAutomatWithOnePepsi

public void testCanBuyWithoutBalance()
{
assertFalse("we cannot buy pepsi without money.", automat.canBuy(pepsi));
}

// class Automat

public boolean canBuy(Pepsi pepsi)

{

return false;

}

我们太喜�Ƣ运行测试了�Q�于是又忍不住运行了所有的自动��试�Q�呵呵，实际上我们只需要点��M��个运行按钮）。又是绿�Ԍ��

好，如果Pepsi的�h格是2元，我们�?块钱试试�?/DIV>

// class Pepsi

public static final int PRICE = 2;

// class TestAutomatWithOnePepsi

public void testCanBuyWithOneYuan()
{

automat.put(1);
assertFalse("we cannot buy pepsi with one yuan.", automat.canBuy(pepsi));
}

// class Automat

public void put(int yuan)

{

}

�q�行��试�Q�绿艌Ӏ�显�?块钱��C��到百事可乐。那��投2块钱吧：

// class TestAutomatWithOnePepsi

public void testCanBuyWithTwoYuan()
{
automat.put(2);
assertTrue("we can not buy pepsi with two yuan.", automat.canBuy(pepsi));
}

�q�行��试�Q�红色进度条�Q?A >JUnit提示“we can not buy pepsi with two yuan.�?天啊�Q�这不公�q��?/DIV>

惌��v来了�Q�Automat.put什么也没做。于是我们添了几�W�：

// class Automat

public void put(int yuan)

{

balance += yuan;

}

public boolean canBuy(Pepsi pepsi)

{

return balance >= Pepsi.PRICE;

}

public int balance = 0; // ��L��了final

�q�不及待地点��M��q�行按钮�Q�yeah�Q�终于能买到喜欢的Pepsi了（因�ؓ看到了绿色进度条～）�?/DIV>

于是急忙��C��一瓶Pepsi�Q?/DIV>

// class TestAutomatWithOnePepsi

public void testBuyPepsiWithTwoYuan()
{
automat.put(2);
automat.buy(pepsi);

assertTrue("the automat should be empty.", automat.isEmpty());
}

// class Automat

public void buy(Pepsi pepsi)

{

}

Run Tests, Failed. So,

// class Automat

public void buy(Pepsi pepsi)

{

goods.remove(pepsi);

}

Run Tests again, OK.

// class TestAutomatWithOnePepsi

public void testBuyPepsiWithTwoYuan()
{
automat.put(2);
automat.buy(pepsi);

assertTrue("the automat should be empty.", automat.isEmpty());
assertEquals("the balance should be 0.", 0, automat.balance);

}

Run Tests, failed, so

// class Automat

public void buy(Pepsi pepsi)

{

goods.remove(pepsi);

balance -= Pepsi.PRICE;

}

Run Tests again, OK.

那如果没有投币就直接买Pepsi呢？再添加一个测试：

// class TestAutomatWithOnePepsi

public void testBuyPepsiWithNoBalance()
{
  try
  {
    automat.buy(pepsi);
    fail("a NoBalanceException was expected when buying a pepsi with no balance.");
  }
  catch (NoBalanceException e)
  {
  }
}

// class NoBalanceException

public class NoBalanceException extends Exception
{
public NoBalanceException(String arg0)
{
super(arg0);
}
}

// class TestAutomatWithOnePepsi

public void testBuyPepsiWithTwoYuan()
{
  automat.put(2);
  try
  {
    automat.buy(pepsi);
  }
  catch (NoBalanceException e)
  {
    fail("a NoBalanceException was throwed.");
  }
assertTrue("the automat should be empty.", automat.isEmpty());
  assertEquals("the balance should be 0.", 0, automat.balance);
}

// class Automat

public void buy(Pepsi pepsi) throws NoBalanceException
{
if (balance == 0)

    throw new NoBalanceException("No balance");
  else if (balance >= Pepsi.PRICE)
  {
    goods.remove(pepsi);
  balance -= Pepsi.PRICE;
  }
}

�q�行��试�Q�绿�Ԍ��

接下来投1块钱��C��看：

// class TestAutomatWithOnePepsi

public void testBuyPepsiWithOneYuan()
{
  automat.put(1);
  try
  {
    automat.buy(pepsi);
    fail("a LackOfBalanceException was expected when buying a pepsi without enough balance.");
  }
  catch (LackOfBalanceException e)
  {
  }
  catch (NoBalanceException e)
  {
   fail("a NoBalanceException was not expected.");
  }
}

接下来，��Z��能�ɾ~�译通过�Q�做了一下修改：

// class LackOfBalanceException

public class LackOfBalanceException extends Exception
{
public LackOfBalanceException(String arg0)
{
super(arg0);
}
}

// class Automat

public void buy(Pepsi pepsi) throws NoBalanceException, LackOfBalanceException
{

// ...

}

// class TestAutomatWithOnePepsi

public void testBuyPepsiWithNoBalance()
{

// ...
  catch (LackOfBalanceException e)
  {
    fail("a LackOfBalanceException was not expected.");
  }
}

public void testBuyPepsiWithTwoYuan()
{
// ...

  catch (LackOfBalanceException e)
  {
  fail("a LackOfBalanceException was not expected.");
  }
  // ...
}

好，没有错误提示了。编译，�q�行��试�Q�红色进度条�?/DIV>

testBuyPepsiWithOneYuan()提示“a LackOfBalanceException was expected when buying a pepsi with no enough balance."

我们修改一下Automat.buy()�Q?/DIV>

// class Automat

public void buy(Pepsi pepsi) throws NoBalanceException, LackOfBalanceException
{
  if (balance == 0)
  {
  throw new NoBalanceException("No balance");
  }
  else if (balance >= Pepsi.PRICE)
  {
   goods.remove(pepsi);
    balance -= Pepsi.PRICE;
  }
  else
    throw new LackOfBalanceException("Lack of Balance");
}

��试通过了！��小庆祝一下～

那如果我们投了三块钱呢？好，试试看：

// class TestAutomatWithOnePepsi

public void testBuyPepsiWithThreeYuan()
{
  automat.put(3);
  assertTrue("we can buy pepsi.", automat.canBuy(pepsi));
  try
  {
   automat.buy(pepsi);
    assertTrue("the automat should be empty.", automat.isEmpty());
    assertEquals("the balance should be 1.", 1, automat.balance);

}

  catch (Exception e)
  {
  fail("Exception was not expected.");
  }
}

�~�译�Q�运行测试，成功�Q�Yeah!

To be continued...

下一集将会更加精彩，敬请期待�?/DIV>

Baoquan Inside 2006-02-25 23:12 发表评论

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���试驱动开发案例之自动售货机（�W?集）

��试驱动开发案例之自动售货机（�W?集）