Add Docker containers to help development against local DBs

CONTRIBUTING.md

@@ -24,3 +24,15 @@ just test
 ```
 
 If you don't have `just` installed, you can look in the `justfile` for the commands that are run.
+
+To help with testing on Docker, there's a `docker-compose.yml` file to run PostgreSQL and MySQL in Docker, as well as some additional `just` commands for testing:
+
+```sh
+just start-dbs
+just test-postgres
+just test-mysql
+just test-sqlite
+
+# To run all of the above:
+just test-dbs
+```

docker-compose.yml

@@ -0,0 +1,16 @@
+services:
+  postgresql:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+    ports:
+      - 15432:5432
+
+  mysql:
+    image: mysql:8.4
+    environment:
+      MYSQL_ROOT_PASSWORD: django
+      MYSQL_DATABASE: django
+    ports:
+      - 13306:3306

justfile

@@ -17,3 +17,18 @@ lint:
     python -m ruff check django_tasks tests
     python -m ruff format django_tasks tests --check
     python -m mypy django_tasks tests
+
+start-dbs:
+    docker-compose pull
+    docker-compose up -d
+
+test-sqlite *ARGS:
+    python -m manage test --shuffle --noinput {{ ARGS }}
+
+test-postgres *ARGS:
+    DATABASE_URL=postgres://postgres:postgres@localhost:15432/postgres python -m manage test --shuffle --noinput {{ ARGS }}
+
+test-mysql *ARGS:
+    DATABASE_URL=mysql://root:django@127.0.0.1:13306/django python -m manage test --shuffle --noinput {{ ARGS }}
+
+test-dbs *ARGS: start-dbs test-postgres test-mysql test-sqlite