Test::Database::Tutorial(3pm) User Contributed Perl Documentation Test::Database::Tutorial(3pm)
NAME
Test::Database::Tutorial - How to use Test::Database
INTRODUCTION
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:
o using SQLite
No setup needed, but the test script can only use SQLite's dialect of SQL. So much for portability across database engines.
o 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.
o 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).
o 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:
o getting DSN information from a list of pre-configured database and engines
o automatic detection of "file-based" database engines (typically, SQLite).
The rest of this document describes various use cases for "Test::Database".
MODULE AND TEST AUTHOR
"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 optionaly 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:
o either a handle to a newly created database (created especially at the test script's request)
o 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")'
DBM
SQLite
mysql
With no parameter, it will return the list of configured ones:
$ perl -MTest::Database -le 'print for Test::Database->list_drivers()'
DBM
SQLite
CPAN TESTER
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 "
", $_->name, $_->databases for Test::Database->drivers'
Example output:
CSV
tdd_csv_book_0
tdd_csv_book_1
DBM
SQLite
tdd_sqlite_book_0
tdd_sqlite_book_1
SQLite2
tdd_sqlite2_book_0
mysql
tdd_mysql_book_0
tdd_mysql_book_1
The following one-liner will drop them all:
perl -MTest::Database -le 'for$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.
ADDING SUPPORT FOR A NEW DATABASE ENGINE
"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".
WHERE DO DSN COME FROM
?
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:
o "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.
o "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.
o 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.
AUTHOR
Philippe Bruhat (BooK), "<book@cpan.org>"
COPYRIGHT
Copyright 2009-2010 Philippe Bruhat (BooK), all rights reserved.
LICENSE
You can redistribute this tutorial and/or modify it under the same terms as Perl itself.
perl v5.10.1 2010-11-27 Test::Database::Tutorial(3pm)