My preferred way of launching a test X server for WM experimentation

xephyrize.sh

#!/bin/bash
# Usage: ./xephyrize 2bwm|dwm|cwm|tinywm

# Define a simple X session
function x_session() {
    sleep 1;
    $@ &
    xterm &
}

# launch the nested X server
Xephyr +extension RANDR -screen ${SCREEN_SIZE:-800x600} :1 -ac &

# pass our arguments into the x_session
DISPLAY=:1 x_session $@ &

# wait for everyone in our shell's process group to exit
wait