fix(db): check for graph_executions table before dropping

This is needed to not fail tests; see comment in code.

invokeai/app/services/shared/sqlite_migrator/migrations/migration_5.py

@@ -15,19 +15,43 @@ class Migration5Callback:
     def _drop_graph_executions(self, cursor: sqlite3.Cursor) -> None:
         """Drops the `graph_executions` table."""
 
+        # Check if the table exists first. This shouldn't ever be an issue for users, but it is for tests.
+        #
+        # Unlike other database tables, whose schemas are managed by the migrator, `graph_executions`
+        # is created and managed by an instance of `SqliteItemStorage``. Specifically, it is created in the
+        # `__init__` of `SqliteItemStorage`.
+        #
+        # In tests, we don't always create an instance of `SqliteItemStorage`, so the table may not exist in
+        # the test memory db fixture.
+        #
+        # We _do_, however, run the migrator on the test memory db fixtures. So, we need to check if the
+        # table exists before dropping it, else unrelated tests will fail.
+        #
+        # This song and dance won't be necessary again, because we aren't using `SqliteItemStorage` for anything
+        # moving forward.
+
         cursor.execute(
             """--sql
-            SELECT COUNT(*) FROM graph_executions;
+            SELECT name FROM sqlite_master WHERE type='table' AND name='graph_executions';
-            """
-        )
-        count = cast(int, cursor.fetchone()[0])
-        self._logger.info(f"Clearing {count} old sessions from database")
-        cursor.execute(
-            """--sql
-            DROP TABLE IF EXISTS graph_executions;
             """
         )
 
+        if cursor.fetchone():
+            cursor.execute(
+                """--sql
+                SELECT COUNT(*) FROM graph_executions;
+                """
+            )
+            count = cast(int, cursor.fetchone()[0])
+            self._logger.info(f"Clearing {count} old sessions from database")
+            cursor.execute(
+                """--sql
+                DROP TABLE IF EXISTS graph_executions;
+                """
+            )
+        else:
+            self._logger.info("No 'graph_executions' table found.")
+
 
 def build_migration_5(logger: Logger) -> Migration:
     """