Testing Python and PostgreSQL on Multiple Platforms

I’m working on making the Pyrseas functional tests portable enough so that they can be submitted to the repository.

Until now, these tests —which exercise dbtoyaml and yamltodb directly— existed as Linux shell scripts. Briefly, each test runs both dbtoyaml and pg_dump -s on a source database creating YAML and SQL dump outputs, respectively. Then it runs yamltodb on a second dabase to recreate the source tables, etc., and finishes by comparing the first pg_dump ouput to that from the target database to verify that all database objects are present and identical.

The Pyrseas unit tests now use tox which makes it fairly easy to add new platforms. For example, on the Python side, the tox.ini configuration includes 2.7 and 3.2, using a single virtualenv for each version.  It would be easy to add 2.6 or 3.3 (when that is released or from a 3.3.0 rc1 install). To test against Postgres 8.4, 9.0, 9.1 and recently 9.2rc1, the only requirement is to define environment variables PG(84|90|91|92)_PORT with the port numbers used for those Postgres installations. Then tox takes care of running the tests eight times, using each Python/Postgres combination.

Although I have not yet personally run the unit tests on Windows or Linux/Unix variants other than Debian, I believe the tox setup should be quite portable (assuming multiple Postgres installations can be present on a given platform), since the tests only depend on Python and psycopg2 being able to connect to Postgres, i.e., they do not depend on running any PG utilities from the command line.

For the functional tests, running the Pyrseas utilities can be done in a fairly portable way thanks to the os.path, tempfile and subprocess modules. Even the diffing of the pg_dump output can be implemented without having to worry about the presence of a diff command, e.g., on Windows.

However, executing pg_dump against multiple Postgres clusters is not so easy. On Debian (and presumably Ubuntu and all other Debian derivatives), if installed from Debian packages, Postgres utilities can be invoked, for example, as

$ pg_dump --cluster 9.1/main -s pyrseas_testdb

The --cluster option causes the correct executable, e.g., /usr/lib/postgresql/9.1/bin/pg_dump to be run and using the correct port. This translates to Python as:

subprocess.call(['pg_dump', '--cluster 9.1/main', '-s',
                targdump, TEST_DBNAME])

The second element in the list could be provided programmatically to run the tests against various Postgres versions, but it would only work on Debian, Ubuntu, etc. (it also assumes the default cluster installation location).

For Red Hat variants, *BSD or Windows, the only solution I could come up with is requiring the existence of a shell script or .bat file with a set name, e.g., pg_dumpXX, where XX is the PG version number, somewhere along the PATH, to point to the right executable. That is not ideal so I’d appreciate hearing from others who may have dealt with similar issues.

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