If the hard-coded coordinates in the /setblock or the /testforblock commands are negative, the block will be placed one block closer to x=0,z=0 in those coordinates. (happens with player-written commands & command blocks)

for example;
"/setblock -245 89 -98 1 0 clear" will place a stone block at x=-244,y=89,z=-97
"/testforblock -5 4 -5 1 0" will test for a stone block at x=-4,y=4,z=-4 (the previous output will actually say "the block at -4,4,-4")
"/setblock -1 64 -1 137" is the same as "/setblock 0 64 0 137"