hg debuginstall
$ hg debuginstall
Checking encoding (ascii)...
Checking installed modules (*/mercurial)... (glob)
Checking templates...
Checking commit editor...
Checking username...
No problems detected
hg debuginstall with no username
$ HGUSER= hg debuginstall
Checking encoding (ascii)...
Checking installed modules (*/mercurial)... (glob)
Checking templates...
Checking commit editor...
Checking username...
no username supplied (see "hg help config")
(specify a username in your configuration file)
1 problems detected, please check your install!
[1]