test(e2e/mst): DESCRIBE QUERY is now allowed in transactions (#836)

test(e2e/mst): DESCRIBE QUERY now allowed in transactions

The server's MSTCheckRule allowlist has broadened to include DESCRIBE
QUERY (DescribeQueryCommand), mirroring the earlier SHOW COLUMNS change.
It no longer throws inside an active transaction, so the prior
test_describe_query_blocked assertion (DID NOT RAISE) was stale.

Flip it to test_describe_query_not_blocked using _assert_not_blocked
(verifies it succeeds and returns >0 rows) and move DESCRIBE QUERY from
the Blocked to the Allowed list in the class docstring.

Verified against a live DBSQL warehouse: the full TestMstBlockedSql
class (9 tests) passes.

Signed-off-by: Vikrant Puppala <vikrant.puppala@databricks.com>

Author: vikrantpuppala

tests/e2e/test_transactions.py

@@ -565,17 +565,19 @@ class TestMstBlockedSql:
     "Only SELECT / INSERT / MERGE / UPDATE / DELETE / DESCRIBE TABLE are supported."
 
     The server has since broadened the allowlist to include SHOW COLUMNS
-    (ShowDeltaTableColumnsCommand), observed on current DBSQL warehouses.
+    (ShowDeltaTableColumnsCommand) and DESCRIBE QUERY (DescribeQueryCommand),
+    observed on current DBSQL warehouses.
 
     Blocked (throw + abort txn):
     - SHOW TABLES, SHOW SCHEMAS, SHOW CATALOGS, SHOW FUNCTIONS
-    - DESCRIBE QUERY, DESCRIBE TABLE EXTENDED
+    - DESCRIBE TABLE EXTENDED
     - SELECT FROM information_schema
     - Thrift Get{Catalogs,Schemas,Tables,Columns} RPCs (see TestMstMetadata)
 
     Allowed:
     - DESCRIBE TABLE (basic form)
     - SHOW COLUMNS
+    - DESCRIBE QUERY
     """
 
     def _assert_blocked_and_txn_aborted(self, mst_conn_params, fq_table, blocked_sql):
@@ -652,10 +654,14 @@ def test_show_columns_not_blocked(self, mst_conn_params, mst_table):
             mst_conn_params, fq_table, f"SHOW COLUMNS IN {fq_table}"
         )
 
-    def test_describe_query_blocked(self, mst_conn_params, mst_table):
-        """DESCRIBE QUERY is blocked in MST (DescribeQueryCommand)."""
+    def test_describe_query_not_blocked(self, mst_conn_params, mst_table):
+        """DESCRIBE QUERY succeeds in MST — now allowed by the server's MSTCheckRule allowlist.
+
+        Previously blocked (DescribeQueryCommand), the server has since broadened
+        the allowlist to include it, mirroring the earlier SHOW COLUMNS change.
+        """
         fq_table, _ = mst_table
-        self._assert_blocked_and_txn_aborted(
+        self._assert_not_blocked(
             mst_conn_params,
             fq_table,
             f"DESCRIBE QUERY SELECT * FROM {fq_table}",