rjbs forgot what he was saying

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Test::PgMonger, which you should probably not use

by rjbs, created 2016-05-14 13:52
tagged with: @markup:md journal perl programming

JMAP is a protocol that is meant to replace IMAP, CalDAV, CardDAV, SMTP, ACAP (ha ha), and probably some other protocols that aren't springing to mind. Like IMAP, it's meant to make it easy to synchronize offline work with an authoritative server. It does this by dividing up the data model into collections of discrete types, with each collection in a known and addressable state.

I'm not writing this post to talk about JMAP itself, though.

The JMAP model can be useful for things other than email, contacts, and that sort of thing. Why not make other things syncable in the same way? I've been writing a library to make this easy (or at least less difficult) to do. Given a DBIx::Class schema, my library Ix constructs a JMAP-like method dispatcher as well as a Plack application to publish it.

Ix is not even remotely ready for doing real work, so I'm not writing this post to talk about Ix, either.

Since an Ix application uses a database for storing all its entities, its test suite needed a database. I started out by using my usual strategy for testing simple database stuff: SQLite! I love SQLite. It is great. For each test, I could make a new SQLite database, deploy the DBIx::Class schema, and run tests. Then I'd delete the file. Done!

As the SQL that I was generating got more complex, I realized that using SQLite was no longer a good idea. It was great for getting started, but now I needed to run my tests against the same setup I'd have in production. I installed postgresql on my testing box and Postgres.app on my laptop. (By the way, have you seen Postgres.app? It runs Postgres, as you, on your Mac, just like a normal OS X app. It puts a elephant in the menu bar. Neat!) I still needed something to create and destroy my Postgres databases, though, since they weren't just files anymore.

I had a look at Test::Database, but it didn't do what I needed. I'll write (at least to BooK!) about the specific problems, but basically Test::Database's view of test databases is that they aren't nearly as single-use or disposable as what I wanted, and it wasn't easy to extend. Eventually, I wrote my own dumb little library, inspired by parts of Test::Database. It is called Test::PgMonger (pronounced "pig monger"), and it's stupid and effective.

The PgMonger object has credentials to PostgreSQL with permissions to create new users and databases. For now, I'm just assuming that localhost is trusted and I can use the postgres user. It uses those credentials to create a new user and a new database under a unique prefix. That database gets cleaned up at program exist, and there's a way to tell the PgMonger to kill all the databases that match its creating pattern, in case some escape deletion due to crashes or other screw-ups.

This is a really simple hunk of code, and even so it needs more refinement. Hopefully Test::Database can pick up the things I need so that I'm freed from thinking about this one-off thing. For now, though, this has made my testing really painless!