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4。 Rename the file Translator。vb。
5。 Click Add to create the file and add it to your project。
Notice how quickly you managed to create a Visual Basic class using the IDE。 The speed of
creating a class file lets you focus on adding source code to the file。 But do not be misled into
believing that by creating a number of class files； your code will automatically work and be a
masterpiece。 You still need to think about which files； projects； classes； and tests to create。
Translating Hello
The first feature we will implement is the translation of the text “hello。” Since “hello” is English；
the first translation will be English to German。 The following is the code to implement this
feature。 It is added to the Translator。vb file in the LanguageTranslator project。
Public Class Translator
Public Shared Function TranslateHello（ByVal input As String） As String
If （input。pareTo（〃hello〃） = 0） Then
Return 〃hallo〃
ElseIf （input。pareTo（〃allo〃） = 0） Then
Return 〃hallo〃
End If
Return
End Function
End Class
Translator is the main class that is exposed to other ponents or pieces of source code。
Think of it as the identifier of the black box。 The black box has a single method： TranslateHello（）。
TranslateHello（） is used to convert the French “allo” and the English “hello” to the German
“hallo。” The method’s input is a String type； which is a reference object type。
In the implementation of TranslateHello（）； we pare the contents of the input buffer
to the parameter 〃hello〃。 If the parison is equal； meaning that the strings are equal； 0 is
returned。 As you’ll learn in the “Investigating the String Type” section； String is a class that can
be used to create objects； and objects typically have methods。 One of the String type’s methods
is pareTo（）。 The caller of TranslateHello does not know how you managed to translate one
word to another language。 The caller actually does not care； it cares only that the method behaves
as expected。
The abstract intent of the TranslateHello（） method is to accept some text and； if the text
is matched； return a German “hallo。”
Creating the Test Application
Without questioning the abstract intent； the written code needs some testing。 The test code is
added to the test application； which is the project TestLanguageTranslator。
The following code is added to the Module1。vb file。 Remember to import the
LanguageTranslator namespace； otherwise； the test code will not pile。
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54 CH AP T E R 3 ■ L E A R N IN G AB OU T ST R I N G M A N I P U L AT IO N S
Imports LanguageTranslator
Module Module1
Private Sub TestTranslateHello（）
If （Translator。TranslateHello（〃hello〃）。pareTo（〃hallo〃） 0） Then
Console。WriteLine（〃hello to hallo test failed〃）
End If
If （Translator。TranslateHello（〃allo〃）。pareTo（〃hallo〃） 0） Then
Console。WriteLine（〃allo to hallo test failed〃）
End If
If （Translator。TranslateHello（〃allosss〃）。pareTo（〃〃） 0） Then
Console。WriteLine（〃Verify nontranslated word test failed〃）
End If
If （Translator。TranslateHello（〃 allo〃）。pareTo（〃hallo〃） 0） Then
Console。WriteLine（〃Extra whitespaces allo to hallo test failed〃）
End If
End Sub
Sub Main（）
TestTranslateHello（）
Console。ReadKey（）
End Sub
End Module
The source code contains four tests。 Each calls the method TranslateHello（） with some
input and receives the output。 The test happens when the output is verified against an expected
result。 The verification tests use the pareTo（） function to test for correct translation。
Notice the third test：
If （Translator。TranslateHello（〃allosss〃）。pareTo（〃〃） 0） Then
Console。WriteLine（〃Verify nontranslated word test failed〃）
End If
This test expects an explicit failure。 You need to write tests that expect to fail。 Successful
tests that are meant to fail ensure that your code does not generate false positives。 A false positive is
when your code is supposed to fail and it does not。
The tests are within a method that needs to be called from the Main（） method； as in the
following example：
Sub Main（）
TestTranslateHello（）
Console。ReadKey（）
End Sub
If you pile and run the tests； you will find that one of the tests fails。 The failing test is
the fourth one； which attempts to translate a word that has whitespace。 Whitespace is space
that we humans don’t notice； but is necessary to distinguish words； sentences； and so on。 Before
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CH AP T E R 3 ■ L E AR N IN G AB O U T ST R I N G M A N I PU L A TI O N S 55
we can solve the whitespace problem； we need to determine which part of the application is
not working properly。
Answering the Question of Responsibility
The whitespace problem is an interesting one。 The caller explicitly put in the extra spaces； but
is the whitespace a bug； or is it data that is passed in incorrectly？
The problem can be defined in the context of reasonable usage。 Imagine that you’ve just
bought a car and you’re driving it on the highway。 If the car breaks down； the warranty will be
in effect and cover the costs of the car repair。 Now imagine the situation where you think you
are one of the Dukes from the Dukes of Hazzard。 And being a Duke； you drive your new car as
fast as you can and then perform a flying jump。 The car will jump into air； which looks quite
spectacular； but then the car lands。 After that； the shocks collapse； and the car cannot be driven
any further。 Even though the car is brand new； the Duke did not use the car as envisioned by
the car manufacturer； and thus invalidates the warranty。
Getting back to the translation ponent； it exposes the method TranslateHello（） and
has responsibilities。 And the caller of TranslateHello（） has the responsibility of being reason
able about what can be expected to be translated。 So； is whitespace sent by the caller reasonable？
If the whitespace is a normal circumstance； then the failed test is a bug in the ponent。
But if the whitespace is not a normal circumstance； the caller is wrong and must be fixed。 The
answer is that the caller is being reasonable； and the ponent is not acting properly。 We
have a bug in the ponent that needs to be fixed。 How do I know that the caller is not being
reasonable？ I made it up； because that is how I expected the contract to be implemented。 The
key is in defining a good contract。
The bug in the ponent relates to the problem of how a word is being translated。 We
used the pareTo（） method； which means that each character is pared； position for
position。 The test failed because the caller passed in a string with whitespace； and the ponent
expected no whitespace。 This bug is not a surprise； because we humans ignore the whitespace； but
puters cannot。
Before I explain how to fix the bug； I need to take a step back and talk about what a string
is and how you can figure out what a string can do。
Investigating the String Type
String is a class ty