test(postgres): set socketDir with empty listen_addresses

Test a postgres service with socketDir set and empty listen_addresses.

nix/postgres/postgres_test.nix

@@ -16,8 +16,19 @@
       }
     ];
   };
+  services.postgres."pg3" = {
+    enable = true;
+    socketDir = "./test/new/socket/path2";
+    listen_addresses = "";
+    initialDatabases = [
+      {
+        name = "test-db";
+      }
+    ];
+  };
   # avoid both the processes trying to create `data` directory at the same time
   settings.processes."pg2-init".depends_on."pg1-init".condition = "process_completed_successfully";
+  settings.processes."pg3-init".depends_on."pg2-init".condition = "process_completed_successfully";
   settings.processes.test =
     let
       cfg = config.services.postgres."pg1";
@@ -37,12 +48,16 @@
 
           # schemas test
           echo "SELECT * from users where user_name = 'test_user';" | psql -h 127.0.0.1 -p 5433 -d sample-db | grep -q test_user
+         
+          # listen_addresses test
+          echo "SELECT 1 FROM pg_database where datname = 'test-db';" | psql -h "$(readlink -f ${config.services.postgres.pg3.socketDir})" -d postgres | grep -q 1
         '';
         name = "postgres-test";
       };
       depends_on = {
         "pg1".condition = "process_healthy";
         "pg2".condition = "process_healthy";
+        "pg3".condition = "process_healthy";
       };
     };
 }