diff --git a/tests/test_postgres.py b/tests/test_postgres.py
index d54f263d..58b0dbfc 100644
--- a/tests/test_postgres.py
+++ b/tests/test_postgres.py
@@ -15,52 +15,33 @@
 
 
 def _get_db_service_name(dc: DockerClient) -> str:
-    """
-    Use python-on-whales to retrieve the final Compose configuration
-    and return the DB service name that ends with '-db'.
-    Fallback to any service containing 'db' or 'postgres'.
-    Finally, fallback to 'db'.
-    """
     config_data = dc.compose.config()
 
-    if ComposeConfig and isinstance(config_data, ComposeConfig):
-        services_dict = {s.name: s for s in config_data.services}
+    # (1) En versiones nuevas de python-on-whales
+    #     config_data es ComposeConfig => config_data.services es un dict:
+    #       { "nombre_servicio": ServiceConfig(...) }
+    # (2) En versiones viejas => config_data es un dict "legacy"
+    #       => config_data["services"] => { "nombre_servicio": {...} }
 
-    elif isinstance(config_data, dict):
-        services_dict = config_data["services"]
+    if ComposeConfig and isinstance(config_data, ComposeConfig):
+        services_dict = config_data.services  # <--- OJO: NO iterar con s.name
     else:
-        raise TypeError(
-            f"dc.compose.config() devolvió un tipo inesperado: {type(config_data)}"
-        )
-    for svc_name in services_dict:
-        if svc_name.lower().endswith("-db"):
-            return svc_name
-    for svc_name in services_dict:
-        lower_svc_name = svc_name.lower()
-        if "postgres" in lower_svc_name or "db" in lower_svc_name:
-            return svc_name
-    return "db"
+        # Versión vieja => dict con clave "services"
+        services_dict = config_data["services"]
 
+    # Ahora "services_dict" es { "nombre_servicio": ... } en todos los casos
 
-def _get_db_service_name(dc: DockerClient) -> str:
-    """
-    Use python-on-whales to retrieve the final Compose configuration
-    and return the DB service name that ends with '-db'. Fallback to
-    any service containing 'db' or 'postgres'. Finally, fallback to 'db'.
-    """
-    config_data = dc.compose.config()  # Returns a dict with { "services": {...}, ... }
-    services_dict = config_data["services"]
-    # First pass: Look for a service name that exactly ends with '-db'
+    # 1ª pasada: servicio que termine con -db
     for svc_name in services_dict:
         if svc_name.lower().endswith("-db"):
             return svc_name
 
-    # Second pass: Fallback to any name containing 'db' or 'postgres'
+    # 2ª pasada: cualquier servicio que contenga db o postgres
     for svc_name in services_dict:
         if "postgres" in svc_name.lower() or "db" in svc_name.lower():
             return svc_name
 
-    # Final fallback
+    # 3ª pasada: fallback
     return "db"