I would mention that if you read the man page it does have a good little example about using the -p option, but the breakdown is that it strips off leading slashes based on the value assigned (ie, 0 would be the full path and 1 would make it relative to the current directory and so on). So depending on where you call the patch from (where the actual patch file is is irrelevant) you need
the path to the file to be patched to be the same. So in your example you could put a boot directory in your test directory and place the file to be changed in there and create the patch.
the issue then becomes if you set it to 1 and as boot sits directly under the root directory, you would need to be calling the path command from within / ... hope that helps a little
