Minecraft – How to use setblock command for placing stone button on the left side of the command block

Here's the structure of the /setblock command:

/setblock x y z block data method [dataTag]

xyz are the coordinates of the block
block is the TileID of the block (includes id:0 now!)
data is the block data (i.e. 5:1 spruce wood)
method is one of three things: keep, replace, or delete

• keep spawns the block at the coordinates.
• replace replaces the block at the coordinates with the block ID.
• delete removes the block at the coordinates and then spawns the new one in

dataTag (optional) is tile entity data.

From Minecraft wiki

You will need to do two things:

• Firstly, there are two other parts to the /setblock command that need to be present; the datavalue, and the method of handling the existing block, if any.
• Secondly, the data tag at the end should just be {Command: "testfor @p[_=1]"}, without the TileEntityData bit.

Thus, the resulting command should be along the lines of

/setblock <x> <y> <z> command_block 0 replace {Command:"testfor @p[_=1]"}

As proof, here's a shot of me using that command:

And here's the result: