Check the server is of type PG and return jsonb

test/CDB_FederatedServerDiagnostics.sql

@@ -1,2 +1,50 @@
+-- ===================================================================
+-- create FDW objects
+-- ===================================================================
+\set QUIET on
+SET client_min_messages TO error;
+\set VERBOSITY terse
+CREATE EXTENSION postgres_fdw;
+
+CREATE ROLE cdb_fs_tester LOGIN PASSWORD 'cdb_fs_passwd';
+GRANT CONNECT ON DATABASE contrib_regression TO cdb_fs_tester;
+
+-- Create database to be used as remote
+CREATE DATABASE cdb_fs_tester OWNER cdb_fs_tester;
+
+SELECT 'C1', cartodb.CDB_Federated_Server_Register_PG(server => 'loopback'::text, config => '{
+    "server": {
+        "host": "localhost",
+        "port": @@PGPORT@@
+    },
+    "credentials": {
+        "username": "cdb_fs_tester",
+        "password": "cdb_fs_passwd"
+    }
+}'::jsonb);
+\set QUIET off
+
+
+-- ===================================================================
+-- Test server diagnostics function(s)
+-- ===================================================================
 \echo '%% It raises an error if the server does not exist'
 SELECT '1.1', cartodb.CDB_Federated_Server_Diagnostics(server => 'doesNotExist');
+
+\echo '%% It returns a jsonb object'
+SELECT '1.2', pg_typeof(cartodb.CDB_Federated_Server_Diagnostics(server => 'loopback'));
+
+
+-- ===================================================================
+-- Cleanup
+-- ===================================================================
+\set QUIET on
+SELECT 'D1', cartodb.CDB_Federated_Server_Unregister(server => 'loopback'::text);
+DROP DATABASE cdb_fs_tester;
+
+-- Drop role
+REVOKE CONNECT ON DATABASE contrib_regression FROM cdb_fs_tester;
+DROP ROLE cdb_fs_tester;
+
+DROP EXTENSION postgres_fdw;
+\set QUIET off

test/CDB_FederatedServerDiagnostics_expect

@@ -1,2 +1,6 @@
+C1|
 %% It raises an error if the server does not exist
-1.1|{}
+ERROR:  Server "doesNotExist" does not exist
+%% It returns a jsonb object
+1.2|jsonb
+D1|