Hi Hakar,
I've worked at a university's language center for 2 years and we run placement tests on Moodle. We used the C-Test, which is the most used language assessment method, with high reliability and validity. Unfortunately, there is no integration with Moodle - the last news were this and this. We used a kind of script to easily generate a C-Test and to integrate it in a quiz. It was not a real plugin, though. If you want, I can give you the contact of the person who developed it.
Cheers,
Beatriz
