Installation: see Horde.

Typically 

# mysql setup
apt install php-horde-webmail
webmail-install
# admin user setup

Test suite

For a single plugin package: 

apt install autopkgtest
adt-run -B ./ --- null  # jessie
autopkgtest -B -- null  # stretch

or manually: 

apt install php-horde-test
quilt push -a
cd Horde_Text_Filter-*/test/Horde/Text/Filter/
phpunit .