Re: Writing unit tests in Perl.

[Adam Turoff <ziggy@panix.com>]

> On a more general note concerning XP, I find it difficult to understand how
> one might go about coding by first generating a set of tests and then coding
> until all tests work.  

Here, it's important to keep in mind that the author is a Smalltalk
consultant and has been floating around the OOP community for a number
of years.   With that in mind, think about coding in a C++/Java/Smalltalk
style where everything is an object and you're testing each method
individually.

With that mindset, it should be easier to test your code when it is
properly factored[1] - every method does one "atomic" operation in your
program.  That is, it should be easier to test code that calculates
splines, planetary orbits and gravitational interaction than testing a
monolithic function like shortest_route_to_mars_from_earth().

> The concept is straightforward, but it seems to me
> that the difficult part is knowing when you have the "right" set of tests.
> Maybe it will become clearer once I read the chapter on testing strategy.

To begin with, the "right" sets of tests handle common cases accurately,
exceptional cases properly and border cases appropriately.  This has
obvious implications of you're writing test code for fopen() or sqrt();
it may be more difficult how to apply to real-world code, though.

One interaction within XP  is between testing and refactoring.  Since
you're constantly rewriting existing code on an XP project (using the
pre-existing tests as a validation suite), you can look at tests that
are difficult to write as a indication that your code/design needs to
be refactored.

Z.

[1] This idea has been floating around for over 30 years, possibly 
    dating back to Simula67.  I came across a reference to properly 
    factoring code as far back as 1970: 

    http://www.forth.com/Content/History/History1.htm

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