I'm not convinced I find the first example more readable though:

if assert.For(t).ThatActual(err).IsNil().Passed()

I'm reading this as "assert that the check that err is nil passed". It certainly reads like a sentence but `if err == nil` seems much more idiomatic, is shorter, to me is also easier to write and conveys the same meaning.

That said, 10/10 for having an actually useful README with examples I can work from, and get a feel for what this is supposed to do and how it's supposed to work.