Visual Basic —

Tip 15: Don't test your own software or write your own test plans.

Do you have dedicated testers where you work? Possibly not-not many companies do. Many companies say they "can't afford such a luxury." Well, in my opinion, they're a luxury that's really worth it (as many of the leading software development companies in the world already know).

Independent testers should (and often do) exhibit the following characteristics:

  • Are impartial

  • Are less informed about the usage and the type of input your code expects

  • Are usually more knowledgeable about the usage and the type of input your code doesn't expect

  • Are more likely than you to spend time trying to break code

  • Are typically more leery of your interfaces and more critical of your coupling

  • Are into doing you damage and breaking your code

  • Are more informed than you about system limits

  • Unlike you, actually want to find bugs in your software.

From time to time, Microsoft talks about its ratio of developers to testers: around 1:1. You do the math; for every programmer there's a tester. In fact, rumor has it that some developers occasionally get shifted to being testers. This could happen if a developer consistently develops very buggy software. Nothing like a shift to testing to improve one's knowledge and appreciation of what good solid code involves.

Define constants using a TypeLib or an Enum.

When you create error values try not to use the so-called Magic Numbers. Thirteen is such a number, as in Err.Raise Number:=13. What does 13 mean? Basically it's a pain to resolve, so attempt always to use more meaningful names.

Visual Basic doesn't come with a set of symbolic constants defined for its own errors so I thought I'd put one together for you. Here's a snippet:

Public Enum vbErrorCodes
      VBErrReturnWithoutGoSub                  = 3
      VBErrInvalidProcedureCall                = 5
      VBErrOverflow                            = 6
      VBErrOutOfMemory                         = 7
      VBErrSubscriptOutOfRange                 = 9
      VBErrThisArrayIsFixedOrTemporarilyLocked = 10
      VBErrDivisionByZero                      = 11
      VBErrTypeMismatch                        = 13
      VBErrOutOfStringSpace                    = 14
      VBErrExpressionTooComplex                = 16
      VBErrCantPerformRequestedOperation       = 17
      VBErrUserInterruptOccurred               = 18
      VBErrResumeWithoutError                  = 20
      VBErrOutOfStackSpace                     = 28
      VBErrSubFunctionOrPropertyNotDefined     = 35
      .
      .
      .
  End Enum

Once you've added it to your project, this snippet is browsable via Visual Basic's Object Browser. To see how you might define constants using a type library, see Chapter 7.