van.pg 2.0

Tools to programmatically manage PostgreSQL clusters as Python test fixtures
van.pg is a Python module that provides easy creation of PostgreSQL databases (and clusters) for unit testing.

Dirty Databases

Test databases take a long time to create. In general you need to be a little careful when you decide to delete/recreate a test database fixture.

Also, there seems to be no robust way in PostgreSQL of figuring out if a database was committed to or not.

So van.pg has no choice but to place the responsibility on the you to notify it when a database is dirty. If this isn't done properly, test isolation will be compromised. It's not ideal, but the best we can do.

One exception is if you consistently use the transaction package (http://pypi.python.org/pypi/transaction) to manage database commits. In this case you can ask for the resource to be dirtied whenever a transaction is committed.

Integration with testresources

The typical way to use these fixtures is via testresources (http://pypi.python.org/pypi/testresources/):

 >>> from testresources import ResourcedTestCase
 >>> from van.pg import DatabaseManager
 >>> import psycopg2

 >>> def init_db(db):
 ... conn = psycopg2.connect(host=db.host, database=db.database)
 ... cur = conn.cursor()
 ... cur.execute("CREATE TABLE foo (bar INTEGER);")
 ... conn.commit()
 ... conn.close()


 >>> class MyTest(ResourcedTestCase):
 ...
 ... resources = [('db', DatabaseManager(initialize_sql=init_db))]
 ...
 ... def runTest(self):
 ... conn = psycopg2.connect(host=self.db.host, database=self.db.database)
 ... cur = conn.cursor()
 ... cur.execute("INSERT INTO foo VALUES (1);")
 ... conn.commit()
 ... cur = conn.cursor()
 ... cur.execute("SELECT * FROM foo")
 ... self.assertEquals(cur.fetchall(), [(1, )])
 ... # NOTE: must close connections or dropping databases fails
 ... conn.close()
 ... self.db.dirtied() # we changed the DB, so it needs re-loading


Actually run the test:

 >>> from unittest import TextTestRunner
 >>> import sys
 >>> runner = TextTestRunner(stream=sys.stdout)
 >>> runner.run(MyTest()) # doctest: +ELLIPSIS
 .
 ...
 OK
 ...


Using template databases

If you need to recreate the same database many times, it can be faster to let PostgreSQL copy the database from a template database. You can do this by having one DatabaseManager serve as the template for another:

 >>> template_db = DatabaseManager(initialize_sql=init_db)
 >>> class MyTest2(MyTest):
 ... resources = [('db', DatabaseManager(template=template_db))]

 >>> runner.run(MyTest2()) # doctest: +ELLIPSIS
 .
 ...
 OK
 ...

transaction integration

If the keyword argumen dirty_on_commit is True, a DatabaseManager will mark the database as dirtied after every successfull commit made through the transaction module. This means each test which dirties the database does not have to manually notify it.

 >>> man = DatabaseManager(dirty_on_commit=True)

If you use this feature, you need to depend on the transaction (http://pypi.python.org/pypi/transaction) package yourself.

Using an existing database

By default, van.pg creates a new PostgreSQL cluster in a temporary directory and launches a PostgreSQL daemon. This works most of the time, but is not very fast.

If you have an already running PostgreSQL cluster, you can tell van.pg to use it by setting the environment variable VAN_PG_HOST. For example, to run van.pg's tests against a local PostgreSQL server with it's sockets in /tmp/pgcluster do:

VAN_PG_HOST=/tmp/pgcluster python setup.py test

WARNING: any databases starting with test_db in the target database are likely to be dropped.

Closing Connections

Be careful to properly close all connections to the database once your test is done with it. PostgreSQL doesn't allow dropping databases while there are open connections. This will cause van.pg to error when trying to drop the test database.

Programatically creating a cluster

At a lower level, you can also programmatically manipulate your own PostgreSQL cluster.

Initialize the Cluster:

 >>> from van.pg import Cluster
 >>> cluster = Cluster()
 >>> cluster.initdb()


Which creates a database in a temporary directory:

 >>> import os
 >>> dbdir = cluster.dbdir
 >>> 'PG_VERSION' in os.listdir(dbdir)
 True


Start it:

 >>> cluster.start()

Create/Test a database:

 >>> dbname = cluster.createdb()

We can connect to the database:

 >>> import psycopg2
 >>> conn = psycopg2.connect(database=dbname, host=cluster.dbdir)
 >>> cur = conn.cursor()


Twiddle the database to make sure we can do the basics:

 >>> cur.execute("CREATE TABLE x (y int)")
 >>> cur.execute("INSERT INTO x VALUES (1)")
 >>> conn.commit()
 >>> cur.execute("SELECT * from x")
 >>> cur.fetchall()[0][0]
 1


Stop the cluster daemon:

 >>> conn.close()
 >>> cluster.stop()


Start it again:

 >>> cluster.start()
 >>> conn = psycopg2.connect(database=dbname, host=cluster.dbdir)
 >>> cur = conn.cursor()
 >>> cur.execute("SELECT * from x")
 >>> cur.fetchall()[0][0]
 1


And cleanup:

 >>> conn.close()
 >>> cluster.cleanup()
 >>> cluster.dbdir is None
 True
 >>> os.path.exists(dbdir)
 False


Development

Development takes place on GitHub:

 http://github.com/jinty/van.pg

last updated on:
May 16th, 2012, 22:50 GMT
price:
FREE!
homepage:
pypi.python.org
license type:
BSD License 
developed by:
Brian Sutherland
category:
ROOT \ Programming \ Quality Assurance and Testing
van.pg
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What's New in This Release:
  • Support Python 3.2.
  • Drop Python 2.5 support.
  • Add tox.ini for testing against multiple python versions.
  • Run PostgreSQL as a subprocess rather than as a daemon (via pg_ctl).
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