[Docker] Add test service

This can simply be invoced with `docker-compose run tests`.

docker-compose.yml

@@ -1,25 +1,27 @@
 version: "3"
 
+x-environment: &common-env
+  DATABASE_URL: postgresql://danbooru:@postgres
+  DANBOORU_HOSTNAME: http://localhost:3000
+  DANBOORU_REDIS_URL: redis://redis
+  DANBOORU_ELASTICSEARCH_HOST: elastic
+  DANBOORU_MEMCACHED_SERVERS: memcached
+  # These are just development secrets, do not use them in production
+  SECRET_TOKEN: 1c58518a891eff4520cadc59afa9e378a9325f1247544ff258096e497f095f45
+  SESSION_SECRET_KEY: 44b4f44e9f253c406cbe727d403d500c1cecff943e4d2aea8f5447f28846fffe
+
 services:
   e621:
     build: ./
+    image: e621
     volumes:
       - .:/app
       - node_modules:/app/node_modules
       - public_packs:/app/public/packs
-      - public_packs_test:/app/public/packs-test
       - post_data:/app/public/data
     environment:
-      DATABASE_URL: postgresql://danbooru:@postgres
+      <<: *common-env
       RAILS_ENV: development
-      DANBOORU_HOSTNAME: http://localhost:3000
-      DANBOORU_REDIS_URL: redis://redis
-      DANBOORU_ELASTICSEARCH_HOST: elastic
-      DANBOORU_MEMCACHED_SERVERS: memcached
-      DANBOORU_IQDBS_SERVER: http://iqdb:4567
-      # These are just development secrets, do not use them in production
-      SECRET_TOKEN: 1c58518a891eff4520cadc59afa9e378a9325f1247544ff258096e497f095f45
-      SESSION_SECRET_KEY: 44b4f44e9f253c406cbe727d403d500c1cecff943e4d2aea8f5447f28846fffe
     depends_on:
       - postgres
       - redis
@@ -28,13 +30,30 @@ services:
       - iqdb
     tty: true
 
+  tests:
+    image: e621
+    environment:
+      <<: *common-env
+      # Hide annoying output from libvips on corrupt files
+      VIPS_WARNING: "0"
+    volumes:
+      - .:/app
+      - node_modules:/app/node_modules
+    depends_on:
+      - postgres
+      - redis
+      - memcached
+      - elastic
+    entrypoint: ["bundle", "exec", "rails", "test"]
+    profiles:
+      - test
+
   nginx:
     image: nginx:stable-alpine
     volumes:
       - ./public:/app/public
       - post_data:/app/public/data
       - public_packs:/app/public/packs
-      - public_packs_test:/app/public/packs-test
       - ./docker/default.conf.template:/etc/nginx/templates/default.conf.template
     environment:
       NGINX_HOST: localhost