Set up basic CI

.drone.yml

@@ -2,9 +2,26 @@ kind: pipeline
 type: docker
 name: default
 
+services:
+  - name: postgres
+    image: docker.io/library/postgres:17.2
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+
 steps:
-- name: greeting
-  image: alpine
-  commands:
-  - echo hello
-  - echo world
+  - 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