Using static data will make your tests easier to write and easier to maintain - as you noticed - but it will also make your tests unable to find any problem between your module and your database layout which could cause big problems.

I suggest deciding this on a per-test basis:

  • For functions which don't really require DB access, use static data and static results.
  • For functions which do a lot in your DB (which must be cleaned up after the test), create a test-DB and work there. Create the table(s) or data at the beginning of the test and drop the whole thing after the test is done. Depending on how you write it, it may limit you to one simultanus run of each test or a group of tests with use/change the same data, but this isn't a problem in most cases.
  • Some functions do few operations which could be easily reverted should work in their real environment, even if you need to clean up things after the test.
  • You could also redefine subs to make testing easier.

    • Redefining A simple sample: We had a function for error handling which could trigger three levels of action. When running tests and forcing some errors to check if they're detected, many lines were written to the error log on our dev server (no problem), many mails were written to our dev group postbox (annoying) and sometimes even emergency-procedures were started (cost money).
    We solved this by redefining the actual error handling function in the test script:

    [...] # Init tests, prepare everything, etc.
require 'error.inc'; # Here are the regular handling functions defined
+, Log_Error is one of them

our $ErrorText;
our $ErrorLevel;

eval {
 sub Log_Error {
  ($ErrorText,$ErrorLevel) = @_;
  return 1;
 }
};

    [download]
    (I know, this doesn't use modules, but there shouldn't be any difference.)
    This loads the regular handling include (which means you don't run into missing subroutines like you may when faking %INC) and than overrides the subroutine handled by the require'd file with a own. Now, any function which may or may not throw an error could be followed by: 
    # for expected errors:
ok($ErrorText eq 'foo','Error-checking');
ok($ErrorLevel eq 'mail','Error-level-checking');
# for tests which shouldn't trigger one:
ok($ErrorText eq '','Check for errors');

    [download]

    Test-DB Create a environment specially for the test. If you're using SQL, make the DB name or table name(s) configurable and overwrite the configured values with fixed values for the test. Use the DB/environment creation functions you created for your project, so your test environment will be up-to-date everything. Drop everything which is created automatically after running the test. This may be done by "DELETE * FROM Test_Table" which should be easier than searching a real table for the test-created records.

    Make tests self-defining In few cases, you could read things from your systems parameters or databases and make your tests behave based on the things read. I don't have a good example in mind right now, but just think of a test checking for the number of configuration options written to a config file: The test will change each time you add an option, but if you have a reliable source for the options, you could read the list and check if every option defined is really written. This would change the number of tests dynamically, but this is possible. No a good sample, sorry.

    Finally, the answer in most cases should be yes: You need to change your tests on many system changes. More tests mean less trouble, but means updating more files when changing something.

    In reply to Re: Help with design philosophy II: Testing by Sewi
    in thread Help with design philosophy II: Testing by stevieb

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