An Introduction to Test::MockDBI
by Mark Leighton Fisher |

Some Examples

To make:

$dbh = DBI->connect("dbi:AZ:universe", "mortal", "(none)");

fail, add the rule:

$tmd->bad_method("connect", 1,

    "CONNECT TO dbi:AZ:universe AS mortal WITH \\(none\\)");

(where $tmd is the only Test::MockDBI object, which you obtain through Test::MockDBI's get_instance() method).

To make a SQL SELECT failure when using DBI::execute(), use the rule:

$tmd->bad_method("execute", 1,

    "SELECT zip_plus_4 from zipcodes where state='IN'");

This rule implies that:

• The DBI::connect() succeeded().
• The DBI::prepare() succeeded().
• But the DBI::execute() failed as it should.

A common use of direct scalar return values is returning configuration data, such as a U.S. zip code for an address:

$tmd->set_retval_scalar(1,

 "zip5.*'IN'.*'NOBLESVILLE'.*'170 WESTFIELD RD'",

 [ 46062 ]);

This demonstrates using a regular expression, as matching SQL could then look like this:

SELECT

  zip5

FROM

  zipcodes

WHERE

  state='IN' AND

  city='NOBLESVILLE' AND

  street_address='170 WESTFIELD RD'

and the rule would match.

SELECTs that return one or more rows from the database are the common case:

my $counter = 0;                    # name counter

sub possibly_evil_names {

    $counter++;

    if ($counter == 1) {

        return ('Adolf', 'Germany');

    } elsif ($counter == 2) {

        return ('Josef', 'U.S.S.R.');

    } else {

        return ();

    }

}

$tmd->set_retval_array(1,

   "SELECT\\s+name,\\s+country.*possibly_evil_names",

   \&possibly_evil_names);

Using a CODEREF (\&possibly_evil_names) lets you easily add the state machine for implementing a return of two names followed by an empty array (because the code uses fetchrow_array() to retrieve each row). SQL for this query could look like:

SELECT

  name,

  country

FROM

  possibly_evil_names

WHERE

  year < 2000

Summary

Albert Einstein once said, "Everything should be made as simple as possible, but no simpler." This is what I have striven for while developing Test::MockDBI--the simplest possible useful module for testing DBI programs by mocking up the entire DBI.

Test::MockDBI gives you:

• Complete control of DBI return values and database-returned data.
• Returned database values from either direct value specifications or CODEREF-generated values.
• Easy, regex-based rules that govern the DBI's behavior, along with intelligent defaults for the common cases.
• Complete transparency to other code, so the code under test neither knows nor cares that you are testing it with Test::MockDBI.
• Test data tightly bound to test code, which promotes cohesiveness in your testing environment, thereby reducing the chance that your tests might silently fail due to loss of synchronization between your test data and your test code.

Test::MockDBI is a valuable addition to the arsenal of DBI testing techniques.

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