Just to confirm on my own test. I finally got homebrew running and 3dsident. I can confirm that the lcd-test black squares test does not work. All of my screens are TN by 3ds ident, but some get an IPS score from the lcd test. So H0thTr0n was right on in the analysis from my pictures.
It is strange - there is another test I had seen out there using this website - http://www.lagom.nl/lcd-test/black.php
I see different results between the two systems.
Blue Old 3DS XL : I can see the squares starting at number 8 on both screens
Lime Green N3DS : I can see the squares starting...