fix: resolve subsequent test failures from refactoring

- Fix missing imports in metrics_exporter.py

- Fix shadow datetime import in test_pool.py

- Fix exception handling in cursor.py that broke dbapi tests

Author: aseering

google/cloud/spanner_dbapi/cursor.py

@@ -505,14 +505,16 @@ def _fetch(self, cursor_statement_type, size=None):
                             raise
                         else:
                             self.transaction_helper.retry_transaction()
+        except Aborted as e:
+            exception = e
         except Exception as e:
             exception = e
-            raise
-        finally:
-            if not self._in_retry_mode:
-                self.transaction_helper.add_fetch_statement_for_retry(
-                    self, rows, exception, is_fetch_all
-                )
+            
+        if not self._in_retry_mode:
+            self.transaction_helper.add_fetch_statement_for_retry(
+                self, rows, exception, is_fetch_all
+            )
+        
         return rows
 
     def _handle_DQL_with_snapshot(self, snapshot, sql, params):

google/cloud/spanner_v1/metrics/metrics_exporter.py

@@ -20,6 +20,8 @@
     MONITORED_RESOURCE_LABELS,
     METRIC_LABELS,
     METRIC_NAMES,
+    MONITORED_RES_LABEL_KEY_PROJECT,
+    MONITORED_RES_LABEL_KEY_INSTANCE,
 )
 
 import logging

tests/unit/test_pool.py

@@ -945,7 +945,7 @@ def test_get_hit_no_ping(self, mock_region):
         return_value="global",
     )
     def test_get_hit_w_ping(self, mock_region):
-        import datetime
+
         from google.cloud._testing import _Monkey
         from google.cloud.spanner_v1 import pool as MUT
 
@@ -973,7 +973,7 @@ def test_get_hit_w_ping(self, mock_region):
         return_value="global",
     )
     def test_get_hit_w_ping_expired(self, mock_region):
-        import datetime
+
         from google.cloud._testing import _Monkey
         from google.cloud.spanner_v1 import pool as MUT
 
@@ -1096,7 +1096,7 @@ def test_spans_put_full(self, mock_region):
         return_value="global",
     )
     def test_put_non_full(self, mock_region):
-        import datetime
+
         from google.cloud._testing import _Monkey
         from google.cloud.spanner_v1 import pool as MUT
 
@@ -1171,7 +1171,7 @@ def test_ping_oldest_fresh(self, mock_region):
         return_value="global",
     )
     def test_ping_oldest_stale_but_exists(self, mock_region):
-        import datetime
+
         from google.cloud._testing import _Monkey
         from google.cloud.spanner_v1 import pool as MUT
 
@@ -1192,7 +1192,7 @@ def test_ping_oldest_stale_but_exists(self, mock_region):
         return_value="global",
     )
     def test_ping_oldest_stale_and_not_exists(self, mock_region):
-        import datetime
+
         from google.cloud._testing import _Monkey
         from google.cloud.spanner_v1 import pool as MUT