test: add pgAdmin startup queries test for issue #178

Adds a test file to verify pgAdmin startup queries work correctly.
The test covers:
- SELECT version() query
- The CASE expression checking pg_extension for 'bdr' extension
  and pg_replication_slots for replication slot count

Both pg_extension and pg_replication_slots tables are already
implemented in pg_catalog, so these queries now pass.

Author: iPeluwa

datafusion-postgres/tests/pgadmin.rs

@@ -0,0 +1,32 @@
+use pgwire::api::query::SimpleQueryHandler;
+
+use datafusion_postgres::testing::*;
+
+// pgAdmin startup queries from issue #178
+// https://github.com/datafusion-contrib/datafusion-postgres/issues/178
+const PGADMIN_QUERIES: &[&str] = &[
+    // Basic version query (fixed by #179)
+    "SELECT version()",
+    // Query to check for BDR extension and replication slots
+    r#"SELECT CASE
+        WHEN (SELECT count(extname) FROM pg_catalog.pg_extension WHERE extname='bdr') > 0
+        THEN 'pgd'
+        WHEN (SELECT COUNT(*) FROM pg_replication_slots) > 0
+        THEN 'log'
+        ELSE NULL
+    END as type"#,
+];
+
+#[tokio::test]
+pub async fn test_pgadmin_startup_sql() {
+    let service = setup_handlers();
+    let mut client = MockClient::new();
+
+    for query in PGADMIN_QUERIES {
+        SimpleQueryHandler::do_query(&service, &mut client, query)
+            .await
+            .unwrap_or_else(|e| {
+                panic!("failed to run sql:\n--------------\n{query}\n--------------\n{e}")
+            });
+    }
+}