This command wont work if i try it with droppers:/testforblocks 184 56 828 184 56 828 ~ ~ ~4 ~ ~ ~4, i haven't tested it with other blocks!

You have too many sets of coordinates, not a bug. Just do the command with no parameters (/testforblock) and the command usage will show up in red.

Fixed for a future version. MC-57870

I have items in the dropper and im testing if the items in one dropper are the same as another dropper.