it'd be more pythonic to test this as "if not rev_list"

The del() here is bad: content is aliased here, so you will end up modifying in place the argument passed to from_content(), which could be very surprising for the caller. Please copy the dictionary instead (or slice the needed parts of it before returning it further, or equivalent).

This magic 25 value appears in too many places, I've counted at least 3.
Please:

• either use a constant in the relevant module, and use the constant everywhere else
• or use a "sandwich" architecture, in which the default value is set only in the outer functions, and make the inner ones have mandatory (rather than optional) arguments

Default configuration values will be added to this test configuration, right? If so, you can probably avoid setting max_log_revs explicitly here.