+ """Helper for determining persisted state staleness.
+
+ Args:
+ filename: the filename to check
+ limit_seconds: how fresh, in seconds, it must be
+
+ Returns:
+ True if filename was written within the past limit_seconds
+ or False otherwise (or on error).
+
+ >>> import os
+ >>> filename = f'/tmp/testing_persistent_py_{os.getpid()}'
+ >>> os.system(f'touch {filename}')
+ 0
+ >>> was_file_written_within_n_seconds(filename, 60)
+ True
+ >>> import time
+ >>> time.sleep(2.0)
+ >>> was_file_written_within_n_seconds(filename, 2)
+ False
+ >>> os.system(f'/bin/rm -f {filename}')
+ 0
+ >>> was_file_written_within_n_seconds(filename, 60)
+ False