diff --git a/compose.yaml b/compose.yaml
index 475051e..e751a6c 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -41,5 +41,21 @@ services:
       timeout: 5s
       retries: 20
 
+  db-test:
+    image: mysql:5.7
+    profiles: [testing]
+    environment:
+      MYSQL_DATABASE: pollux_test
+      MYSQL_USER: pollux_test
+      MYSQL_PASSWORD: testing
+      MYSQL_ROOT_PASSWORD: testing-root
+    tmpfs:
+      - /var/lib/mysql
+    healthcheck:
+      test: ["CMD-SHELL", "mysqladmin ping -h 127.0.0.1 -uroot -ptesting-root --silent"]
+      interval: 2s
+      timeout: 5s
+      retries: 30
+
 volumes:
   mysql-data:
diff --git a/tests/CreatesApplication.php b/tests/CreatesApplication.php
index 547152f..6aa30b6 100644
--- a/tests/CreatesApplication.php
+++ b/tests/CreatesApplication.php
@@ -17,6 +17,16 @@ trait CreatesApplication
 
         $app->make(Kernel::class)->bootstrap();
 
+        // RefreshDatabase runs migrate:fresh. Refuse cached or overridden
+        // configuration that could point it at the application's database.
+        if (!$app->environment('testing')
+            || config('database.default') !== 'mysql'
+            || config('database.connections.mysql.host') !== 'db-test'
+            || config('database.connections.mysql.database') !== 'pollux_test'
+            || !empty(config('database.connections.mysql.unix_socket'))) {
+            throw new \RuntimeException('Tests require the isolated db-test / pollux_test database. Clear cached configuration before running tests.');
+        }
+
         return $app;
     }
 }