Test::Database::Tutorial(3) How to use Test::Database


The goal of the Test::Database module is to provide easy to use test databases for test scripts that need them.

The problem

Until now, when a test script needed a database, it either used SQLite (or some other easy to setup database), or required some environment variables to be present, or used default credentials, or even set up the database by itself.

Most of those methods have pros and cons:

  • using SQLite

    No setup needed, but the test script can only use SQLite's dialect of SQL. So much for portability across database engines.

  • using environment variables

    The environment variables are different for every module to test, and usually only the main developers/testers know about them. Since most of the CPAN testers probably don't bother setting them up, these modules are most certainly undertested.

  • using default credentials

    Typically using 'root' and '' to connect to the "test" MySQL database, these test script assume a default installation on the host system. These credentials often provide full access to the database engine, which is a security risk in itself (see below).

  • setting up the database by itself

    This method usually uses the default credentials to access an account with enough privileges to create a database. The host system data may be at risk!

A solution: Test::Database

Many modules use a database to store their data, and often support several database engines.

Wouldn't it be nice to be able to test on all the supported databases that are available on the test system? Without breaking (into) anything?

This is the goal of the Test::Database module. It supports:

  • getting DSN information from a list of pre-configured database and engines
  • automatic detection of ``file-based'' database engines (typically, SQLite).

The rest of this document describes various use cases for Test::Database.


Test::Database has a single interface for test authors:

    my @handles = Test::Database->handles( @requests );

@request is a list of ``requests'' for databases handles. Requests must declare the DBD they expect, and can optionally add version-based limitations (only available for drivers supported by Test::Database).

The handles returned are objects of the Test::Database::Handle class.

The data contained in the database is never destroyed or cleaned up by Test::Database, so it's perfectly fine to have a startup script that will setup the necessary tables and test data, several tests scripts that will build and update the data, and a eventually a teardown script that will drop all created tables.

Test::Database can return two types of databases handles:

  • either a handle to a newly created database (created especially at the test script's request)
  • or a handle to an already existing database

There is no way for the test script to tell the difference.

In any case, the database is assumed to provide "DROP TABLE" and "CREATE TABLE" rights, and the test script is by definition allowed to do whatever it pleases with the tables that exist in the database.

Note that Test::Database supports any DSN, not just those for which it has a driver. If your module supports Oracle, you can add 'Oracle' to your list of requests, and if the host owner configured a "dsn" pointing at an Oracle database, then it will be available for your tests.

Specific database support

It is possible to request specific versions of a database engine.

    use Test::Database;
    # request database handles for all available databases
    my @handles = Test::Database->handles();
    # or for only the databases we support
    my @handles = Test::Database->handles(
        { dbd => 'SQLite' },
        { dbd => 'SQLite2' },
        { dbd => 'mysql', min_version => '4.0' },

See Test::Database documentation for details about how to write a request.

Testing on a development box

The first systems on which you are going to test your module are the ones you own. On these system, it's up to you to configure the databases you want to make available.

A typical ~/.test-database configuration file would look like this:

    dsn      = dbi:mysql:database=test
    username = root
    dsn      = dbi:Pg:database=test
    username = postgres
    dsn      = dbi:Oracle:test

There is no need to add "dsn" sections for file-based drivers (at least the ones that have a corresponding Test::Database::Driver), since the module will automatically detect the available ones and create databases as needed.

To find out which of the DBD that Test::Database supports are installed, use the following one-liner:

    $ perl -MTest::Database -le 'print for Test::Database->list_drivers("available")'

With no parameter, it will return the list of configured ones:

    $ perl -MTest::Database -le 'print for Test::Database->list_drivers()'


The main goal of Test::Database from the point of view of a tester is: ``configure once, test everything''.

As a CPAN tester, once you have installed Test::Database, you should edit the local equivalent of ~/.test-database for the user that will be running the CPAN test suites.

dsn versus driver_dsn

"dsn" sections define the information needed to connect to a single database. Any database listed here can be used by any test script that requests it.

"driver_dsn" sections define the information needed to connect to a database engine (a ``driver'') with sufficient rights to run a "CREATE DATABASE" command. This allows Test::Database to create the databases on demand, thus ensuring every test suite will get a specific database.

If you have file-based database engine, there is nothing to setup, as Test::Database is able to detect available file-based engines and use them as needed.

Other database engines like "mysql" and "Pg" require a little more configuration. For example, here's the content of my ~/.test-database configuration file:

    driver_dsn  = dbi:mysql:
    username    = root
    driver_dsn  = dbi:Pg:
    username    = postgres

For "Pg", I had to edit the pg_hba.cong file in /etc to make sure anyone would be able to connect as the "postgres" user, for example.

Several test hosts accessing the same database engine

If you have a large scale testing setup, you may want to setup a single MySQL or Postgres instance for all your test hosts, rather than one per test host.

Databases created by Test::Database::Driver (using a configured "driver_dsn" have a name built after the following template: "tdd_driver_login_n", where driver is the DBD name, login is the login of the user running Test::Database and n a number that

If the same database server is used by several host running Test::Database from the same user account, there is a race condition during with two different host may try to create the a database with the same name. A simple trick to avoid this is to add a "key" section to the ~/.test-database configuration file.

If the "key" entry exists, the template used by Test::Database::Driver to create new databases is "tdd_driver_login_key_n".

Cleaning the test drivers

When given a "driver_dsn", Test::Database will use it to create a database for each test suite that requests one. Some mapping information is created to ensure the same test suite always receives a handle to the same database. (The mapping of test suite to database is based on the current working directory when Test::Database is loaded).

After a while, your database engine may fill up with unused test databases.

All drivers store their mapping information in the system's temporary directory, so the mapping information is relatively volatile, which implies more unused test databases (at least for non file-based drivers, since the file-based drivers store their database files in the system's temporary directory too).

The following one-liner will list all the existing databases that were created by Test::Database in your configured drivers:

    perl -MTest::Database -le 'print join "\n  ", $_->name, $_->databases for Test::Database->drivers'

Example output:


The following one-liner will drop them all:

    perl -MTest::Database -le 'for$d(Test::Database->drivers){$d->drop_database($_)for$d->databases}'

If a "key" has been defined in the configuration, only the databases corresponding to that key will be dropped.


Test::Database currently supports the following DBD drivers: "CSV", "DBM", "mysql", "Pg", "SQLite2", "SQLite".

Adding a new driver requires writing a corresponding Test::Database::Driver subclass, having the same name as the original "DBD" driver.

An example module is provided in eg/MyDriver.pm, and the other drivers can also be used as an example. See also the WRITING A DRIVER FOR YOUR DATABASE OF CHOICE section in the documentation for Test::Database::Driver.


The following ASCII-art graph shows where the Test::Database::Handle objects returned by the "handles()" method come from:

    ,-------------,      ,-------------,      ,--------------,
    |   DSN from  |      | File-based  |      | Drivers from |
    | config file |      |   drivers   |      |  config file |
    '-------------'      '-------------'      '--------------'
           |                   |                      |
           |                   |    ,-----------,     |
           |                   '--->| Available |<----'
           |                        |  drivers  |
           |                        '-----------'
           |                              |
           |              ,-----------,   |
           '------------->| Available |<--'
                          |    DSN    |

Here are a few details about the "handles()" method works:

  • Test::Database maintains a list of Test::Database::Handle objects computed from the DSN listed in the configuration.

    The handles matching the request are selected.

  • Test::Database also maintains a list of Test::Database::Driver objects computed from the list of supported file-based drivers that are locally available and from the list in the configuration file.

    The list of matching drivers is computed from the requests. Each driver is then requested to provide an existing database (using its existing mapping information) or to create one if needed, and returns the corresponding Test::Database::Handle objects.

  • Finally, all the collected Test::Database::Handle objects are returned.

So, without any configuration, Test::Database will only be able to provide file-based databases. It is also recommended to not put DSN or driver information for the file-based database engines that have a corresponding Test::Database::Driver class, since it will cause "handles()" to return several handles for the same database engine.


Philippe Bruhat (BooK), "<[email protected]>"


Copyright 2009-2010 Philippe Bruhat (BooK), all rights reserved.


You can redistribute this tutorial and/or modify it under the same terms as Perl itself.