create concrete ThriftResultSet instead of ResultSet type

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

Author: varun-edachali-dbx

tests/unit/test_fetches.py

@@ -10,6 +10,7 @@
 import databricks.sql.client as client
 from databricks.sql.utils import ExecuteResponse, ArrowQueue
 from databricks.sql.backend.thrift_backend import ThriftDatabricksClient
+from databricks.sql.result_set import ThriftResultSet
 
 
 @pytest.mark.skipif(pa is None, reason="PyArrow is not installed")
@@ -38,9 +39,8 @@ def make_dummy_result_set_from_initial_results(initial_results):
         # If the initial results have been set, then we should never try and fetch more
         schema, arrow_table = FetchTests.make_arrow_table(initial_results)
         arrow_queue = ArrowQueue(arrow_table, len(initial_results), 0)
-        rs = client.ResultSet(
+        rs = ThriftResultSet(
             connection=Mock(),
-            backend=None,
             execute_response=ExecuteResponse(
                 status=None,
                 has_been_closed_server_side=True,
@@ -52,6 +52,7 @@ def make_dummy_result_set_from_initial_results(initial_results):
                 arrow_schema_bytes=schema.serialize().to_pybytes(),
                 is_staging_operation=False,
             ),
+            thrift_client=None,
         )
         num_cols = len(initial_results[0]) if initial_results else 0
         rs.description = [
@@ -84,9 +85,8 @@ def fetch_results(
         mock_thrift_backend.fetch_results = fetch_results
         num_cols = len(batch_list[0][0]) if batch_list and batch_list[0] else 0
 
-        rs = client.ResultSet(
+        rs = ThriftResultSet(
             connection=Mock(),
-            backend=mock_thrift_backend,
             execute_response=ExecuteResponse(
                 status=None,
                 has_been_closed_server_side=False,
@@ -101,6 +101,7 @@ def fetch_results(
                 arrow_schema_bytes=None,
                 is_staging_operation=False,
             ),
+            thrift_client=mock_thrift_backend,
         )
         return rs