ratest

As a verb ratest

is archaic second-person singular of rate.

As an adjective latest is

superlative of late.

As an adverb latest is

superlative of late POS=adverb.

As a noun latest is

the most recent thing, particularly information or news.

As verbs the difference between retest and ratest

is that retest is to test again while ratest is archaic second-person singular of rate.

As a noun retest

is a repeat test.