测试驱动开发案例之自动售货机（第1集）

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

测试驱动开发(TDD, Test Driven Development)是一种很有意思的软件开发方式，本集以较小的步伐体验TDD。

/** A program simulation of an automat.

* Director: Zuo Baoquan

* Contact me:

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

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

引言：

（该问题截取自《面向对象的设计与模式》(Written by Cay Horstmann) Exercise 2.18

设计并实现一个模拟自动售货机的程序。通过给机器投入正确的硬币，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、投入硬币并得到商品。如果没有足够的钱币或由于此商品已销售完毕，则将硬币退回。操作员可以重新备货并将钱币取走。

场景#1

地点：同济大学西南楼

涉众：我，空自动售货机

寝室楼里面刚搬来了一台空的自动售货机，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"，好，看我的：

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

再露一手：

//class Automat

public boolean isEmpty()

{

return true;

}

全部保存，运行测试，呵呵，绿色进度条！测试成功！

好，既然我们还没有投过硬币，那么余额应该是0了～

// class TestEmptyAutomat

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

继续使用我们的法宝：

// class Automat

public final int balance = 0;

运行测试，yeah!

看了一遍测试程序，决定优化一下：

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;
}

再运行一次测试，呵呵，又是绿色！

场景#2

地点：同济大学西南楼

涉众：我，自动售货机(有一瓶百事可乐)

好消息，楼长在自动售货机里面放了一瓶Pepsi。

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

pepsi = new Pepsi(); // 一瓶百事可乐

automat.add(pepsi); // 楼长阿姨放的～
}

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

public Automat automat;

public Pepsi pepsi;
}

接着创建Pepsi类

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

}
}

再给Automat添加add方法：

// class Automat

public void add(Pepsi pepsi)

{

}

好，现在有两个TC(Test Case)了，为了运行两个测试案例，我们来创建一个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;
}
}

编译成功，运行AutomatTests，红色进度条。TestEmptyAutomat绿色，TestAutomatWithOnePepsi红色。呵呵，看来要让add做点事情了。

// class Automat

public void add(Pepsi pepsi)

{

goods.add(pepsi);

}

// 添加一个装Pepsi的数组列表

private final ArrayList goods = new ArrayList();

// 修改isEmpty方法

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

再次运行AutomatTests，呵呵，绿色！我们喜欢！

好，我们再看看Automat的余额：

// class TestAutomatWithOnePepsi

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

运行一遍测试，Ok。

我们还没有投硬币，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;

}

我们太喜欢运行测试了，于是又忍不住运行了所有的自动测试（呵呵，实际上我们只需要点击一个运行按钮）。又是绿色～

好，如果Pepsi的价格是2元，我们投1块钱试试～

// 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)

{

}

运行测试，绿色。显然1块钱买不到百事可乐。那就投2块钱吧：

// class TestAutomatWithOnePepsi

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

运行测试，红色进度条，JUnit提示“we can not buy pepsi with two yuan.” 天啊，这不公平。

想起来了，Automat.put什么也没做。于是我们添了几笔：

// class Automat

public void put(int yuan)

{

balance += yuan;

}

public boolean canBuy(Pepsi pepsi)

{

return balance >= Pepsi.PRICE;

}

public int balance = 0; // 去掉了final

迫不及待地点击了运行按钮，yeah！终于能买到喜欢的Pepsi了（因为看到了绿色进度条～）。

于是急忙买了一瓶Pepsi：

// 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;
  }
}

运行测试，绿色！

接下来投1块钱买买看：

// 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，为了能使编译通过，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，运行测试，红色进度条。

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

我们修改一下Automat.buy()：

// 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");
}

测试通过了！小小庆祝一下～

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.");
  }
}

编译，运行测试，成功！Yeah!

To be continued...

下一集将会更加精彩，敬请期待。

Baoquan Inside 2006-02-25 23:12 发表评论

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测试驱动开发案例之自动售货机（第1集）