Loading offline html files with mechanize

this may be a dumb simple question yet ive googled and cant find out
what im doing wrong

in my unit tests i want to use offline html pages otherwise live pages
content will change and cause my tests to fail.

How do i do this

ive tried agent.get(‘my_filename.html’) and
agent.get_file(‘my_filename.html’) but errors crop up. Ive checked the
ref docs but most classes have no write up yet (nice interface though!)
so im stuck. Can anyone help