Here's how I test new LVM2 builds without interfering with the stable
LVM2 that is running the LV's on my development box.

1) Create a set of loopback devices.

2) Create a new directory to contain the LVM2 configuration files for
this setup. (I use /etc/lvm_loops)

3) Write a suitable lvm.conf file, this goes in the directory you just
created. eg, my /etc/lvm_loops/lvm.conf looks like:

log {
file="/tmp/lvm2_loop.log"
level=9
verbose=0
overwrite=1
}

devices {
scan = "/dev"
filter = ["a/loop/", "r/.*/"]
}


The important thing to note is the devices section which makes sure
that only the loopback devices are considered for LVM2 operations.

4) When you want to use this test setup just set the environment
variable LVM_SYSTEM_DIR to point to your config directory
(/etc/lvm_loops in my case).

5) It's a good idea to do a vgscan to initialise the filters:

export LVM_SYSTEM_DIR=/etc/lvm_loops
./lvm vgscan

where ./lvm is the new build of LVM2 that I'm trying out.

7) Test away. Make sure that you are explicit about which lvm
executable you want to execute (eg, ./lvm if you are in
LVM2/tools).