A brake lever is good if nothing on it is broken and it isn't missing any parts.
Inspect the lever for cracks. If anything is cracked, the lever is no good.
The lever should have some way to attach to the handlebar. This may be a thin metal loop, or a thick plastic loop, but if there is nothing, the lever is no good.
Wherever the lever attaches to the handlebar, there will often be a place for a bolt to go through it to hold it on. If that bolt is missing, the lever is no good. If there is no place for a bolt, the lever is ok (the bolt is somewhere else on the lever).