Problem

The layered fast truncate test files (test_layered_fast_truncate01–17, test_layered_fast_truncate_metadata, test_layered_fast_truncate_replay, test_layered_fast_truncate_stepup_delete) each define their own copies of the same helper methods inline. No shared base class exists; all classes inherit directly from wttest.WiredTigerTestCase.

Duplicated helpers identified:

• setup_leader() — creates the table and populates initial data on the leader instance
• setup_follower() — switches to follower role and optionally populates keys
• visible_keys() — returns all keys visible via a forward table scan
• populate() — inserts keys with placeholder values
• get_stat() — retrieves a WiredTiger statistic
• truncate() / truncate_range() — perform truncate operations with varying bounds
• search_at() / truncate_and_checkpoint() — point lookups and combined truncate+checkpoint operations

Proposed Fix

Extract the common helpers into a shared mixin or base class (e.g. helper_layered_fast_truncate.py) and update all affected test files to inherit from it. Where signatures differ slightly between files, unify them with optional parameters.