Set up extension
  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > debugcommitmessage=
  > EOF

Set up repo
  $ hg init repo
  $ cd repo

Test extension
  $ hg debugcommitmessage
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: test
  HG: branch 'default'
  HG: no files changed
  $ hg debugcommitmessage --config committemplate.changeset.commit.normal.normal="Test Specific Message\n"
  Test Specific Message
  $ hg debugcommitmessage --config committemplate.changeset.commit="Test Generic Message\n"
  Test Generic Message
  $ hg debugcommitmessage commit.amend.normal --config committemplate.changeset.commit="Test Generic Message\n"
  Test Generic Message
  $ hg debugcommitmessage randomform --config committemplate.changeset.commit="Test Generic Message\n"
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: test
  HG: branch 'default'
  HG: no files changed