How to create an upstart process in Ubuntu?

Question

I am trying to create a process to be automatically started and maintained by Ubuntu's upstart (Ubuntu 12.04). I have been looking at this page as well as on this page and I am aware of the upstart cookbook and upstart stanzas. Using especially the information from the first two likes, I did the following to incorporate such a process. First, I created a file /etc/init/testservice.conf with the following content:

# myservice - myservice job file

description "my service description"
author "Me <myself@i.com>"

# Stanzas
#
# Stanzas control when and how a process is started and stopped
# See a list of stanzas here: http://upstart.ubuntu.com/wiki/Stanzas#respawn

# When to start the service
start on runlevel [2345]

# When to stop the service
stop on runlevel [016]

# Automatically restart process if crashed
respawn

# Essentially lets upstart know the process will detach itself to the background
#expect fork

chdir /home/user/testcode

# Start the process
exec python mycommand.py

with some simple dummy python code mycommand.py residing in the directory /home/user/testcode. Checking with initctl list or ps I see that the command is not yet running. Therefore, I tried to start it 'manually' according to this page with

start testservice

which produced the following output

start: Rejected send message, 1 matched rules; type="method_call", sender=":1.88" (uid=1000 pid=9103 comm="start testservice ) interface="com.ubuntu.Upstart0_6.Job" member="Start" error name="(unset)" requested_reply="0" estination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init")

but did not start the process mycommand.py.

What am I doing wrong? How to tell ubuntu and/or upstart to run the command?