The most common and most likely answer to this crossword clue is the 9 letter word PELMANISM
I've seen this crossword clue in Independent
P
E
L
M
A
N
I
S
M
Buddy explains!

The straight part
We know that "memory test" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case memory test = pelmanism.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.
What does PELMANISM mean?
PELMANISM noun- A system of training to improve the memory.
- A memory card game in which a pack of cards is spread out face down and players try to turn up pairs with the same symbol.