Powerful regression tests for your PostgreSQL project

Mark (aka Winsaucerer) here to show you how you can test your PostgreSQL database like a sorcerer. We are going to be using Spawn, a SQL build system supporting migrations and testing. You do not need to be using Spawn for migrations in order to use it for testing. Spawn does not require any extension installed. All you need is the spawn CLI and a psql connection to the database for Spawn to connect through. Spawn was built to solve some migration pains I've experienced, but I happily discovered that when used for testing, it is very powerful. To show you some of that power, we're going to use a contrived database example. It uses golden file testing to determine success. When the test runs, we capture the stdout and stderr output from psql, and compare that to expected output. Testing with Spawn involves these steps: Create a new test with spawn test new <name> and fill out the test steps Check test outputs with spawn test run <name> (or view the SQL that will be sent to psql via spawn test build <name> ) When outputs are as expected, create the golden file with spawn test expect <name> Run the test and compare to expected output with spawn test compare <name> For now, Spawn only supports connecting via psql, which means that you have access to all the features that psql provides. To get started, follow the Spawn install instructions: Install Spawn And then create a new folder on your system, and initialise a new project with a docker compose config ready for us to play with: # inside your new folder: spawn init --docker docker compose up -d You now have a running docker based PostgreSQL database and a spawn.toml file configured to connect to it. We are not assuming that you are using Spawn or any other tool for migrations, so you can manually create and update the database by connecting directly using psql: docker exec -ti postgres-db psql -U postgres Create the database ⚠️ Caution This post is not intended as an example of how to build an orders database. The des