When testing patch for issue2550636, it turns out that none of
the tests in test_indexer.py would run. I don't know what is wrong
but I worked around it by commenting out the import and classes
for the backends that I did not have installed.

I poked at it trying to fix/diagnose the decorators used to prevent
the tests for the missing components from running, but my python-fu
isn't up to it.

My environment was: linux mint 17.3

> ./run_tests.py --debug -r a --verbose --capture=sys test/test_indexer.py
writing pytestdebug information to
/home/rouilj/develop/roundup.dev/roundup.hg/pytestdebug.log
============================= test session starts
==============================
platform linux2 -- Python 2.7.6, pytest-2.8.4, py-1.4.30, pluggy-0.3.1
-- /usr/bin/python
using: pytest-2.8.4 pylib-1.4.30
cachedir: .cache
rootdir: /home/rouilj/develop/roundup.dev/roundup.hg, inifile: 
collected 0 items / 1 skipped 

=========================== short test summary info
============================
SKIP [1]
/home/rouilj/develop/roundup.dev/roundup.hg/test/test_mysql.py:53:
Skipping MySQL tests: (2002, "Can't connect to local MySQL server
through socket '/var/run/mysqld/mysqld.sock' (2)")
========================== 1 skipped in 3.36 seconds
===========================
wrote pytestdebug information to
/home/rouilj/develop/roundup.dev/roundup.hg/pytestdebug.log