The most common and most likely answer to this crossword clue is the 6 plus 2 plus 4 letter word ORDEAL BY FIRE
I've seen this crossword clue in The Guardian
O
R
D
E
A
L
B
Y
F
I
R
E
Buddy explains!
The straight part
We know that "early test of guilt/early test of guilt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case early test of guilt/early test of guilt = ordeal by fire.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.