In the recent snapshot the /testforblocks broke.
It always says that the "Source and destination are not identical"
You can try to use it at a real group of blocks or you can simply try the command:
/testforblocks ~ ~ ~ ~ ~ ~ ~ ~ ~
What this does is compare the coordinate where the command was called, with the coordinate where the command was called, so basically it's comparing a coordinate with itself, and it still says "Source and destination are not identical", and obviously they are identical.