[Tutor] the art of testing

[Serdar Tumgoren]

Hi everyone,
The list recently discussed the virtues of unit testing, and I was
hoping someone could offer some high-level advice and further
resources as I try to apply the TDD methodology.

I'm trying to develop an application that regularly downloads some
government data (in XML), parses the data and then updates a database.
Simple enough in theory, but the problem I'm hitting is where to begin
with tests on data that is ALL over the place.

The agency in question performs little data validation, so a given
field can have a huge range of possible inputs (e.g. - a Boolean field
should be 0 or 1, but might be blank, have a negative number or even
strings like the word 'None').

In such a case, should I be writing test cases for *expected* inputs
and then coding the the parser portion of my program to handle the
myriad of possible "bad" data?

Or given the range of possible inputs, should I simply skip testing
for valid data at the parser level, and instead worry about flagging
(or otherwise handling) invalid input at the database-insertion layer
(and therefore write tests at that layer)?

Or should I not be testing data values at all, but rather the results
of actions performed on that data?

It seems like these questions must be a subset of the issues in the
realm of testing. Can anyone recommend a resource on the types of
tests that should be applied to the various tasks and stages of the
development process?

A friend recommended The Art of Software Testing -- is that the type
of book that covers these issues? If so, can anyone recommend a
suitable alternative that costs less than $100?

As always, I appreciate the advice.

Regards,
Serdar