Set up basic CI

.drone.yml

@@ -5,14 +5,23 @@ name: default
 services:
   - name: postgres
     image: docker.io/library/postgres:17.2
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
 
 steps:
   - name: lint & test
     image: docker.io/library/elixir:1.18.3-otp-27
+    environment:
+      MIX_ENV: test
     commands:
       # Install hex package manager
       - mix local.hex --force
+      # Fetch dependencies
+      - mix deps.get
       # Check for compilation errors & warnings
       - mix compile --warnings-as-errors
       # Check formatting
       - mix format --check-formatted
+      # Run tests
+      - mix test