Am discussing this with the OP on IRC and tabling it for a while so we can better think out the API.

The goal is to let assertEqual(a, b) do straight-comparions of raw bytes, but to give a nice looking diff (possibly translated with line breaks or somesuch) when the test fails.  This will be helpful in testing the email module. 

The current patch requires that assertBytesEqual be exposed and called directly so that a user can specify a split-at argument.  The purpose of that argument is to approximate the line breaking that occurs naturally in text.  The OP does not want to decode the bytes prior to the equality test, but does want a readable diff whenever the bytes represent ascii text.