test(e2e): verify DML cursor.rowcount against a live warehouse (#784)

End-to-end test in TestPySQLCoreSuite exercising INSERT/UPDATE/DELETE on
a real Thrift warehouse and asserting cursor.rowcount reports the exact
affected-row count (3/2/1), then that a following SELECT resets it to -1.
Verified live on dogfood; fails with the fix reverted (rowcount stays -1).

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

Author: vikrantpuppala

tests/e2e/test_driver.py

@@ -455,6 +455,35 @@ def test_create_table_will_return_empty_result_set(self, extra_params):
             finally:
                 cursor.execute("DROP TABLE IF EXISTS {}".format(table_name))
 
+    def test_dml_rowcount(self):
+        """cursor.rowcount reports the affected-row count for DML
+        (INSERT/UPDATE/DELETE) instead of the hardcoded -1, and resets
+        to -1 for a subsequent SELECT (GH #784)."""
+        with self.cursor({}) as cursor:
+            table_name = "table_{uuid}".format(uuid=str(uuid4()).replace("-", "_"))
+            try:
+                cursor.execute("CREATE TABLE {} (n INT)".format(table_name))
+
+                cursor.execute(
+                    "INSERT INTO {} VALUES (1), (2), (3)".format(table_name)
+                )
+                assert cursor.rowcount == 3, f"INSERT rowcount {cursor.rowcount!r}"
+
+                cursor.execute(
+                    "UPDATE {} SET n = n + 1 WHERE n >= 2".format(table_name)
+                )
+                assert cursor.rowcount == 2, f"UPDATE rowcount {cursor.rowcount!r}"
+
+                cursor.execute("DELETE FROM {} WHERE n = 1".format(table_name))
+                assert cursor.rowcount == 1, f"DELETE rowcount {cursor.rowcount!r}"
+
+                # SELECT must reset rowcount to -1 (not leak the DELETE count).
+                cursor.execute("SELECT * FROM {}".format(table_name))
+                assert cursor.rowcount == -1, f"SELECT rowcount {cursor.rowcount!r}"
+                assert len(cursor.fetchall()) == 2
+            finally:
+                cursor.execute("DROP TABLE IF EXISTS {}".format(table_name))
+
     def test_get_tables(self):
         with self.cursor({}) as cursor:
             table_name = "table_{uuid}".format(uuid=str(uuid4()).replace("-", "_"))