Unit tests only result in a code coverage of
However, with system tests (which require /etc/xcauth.accounts based on xcauth.accounts.sample and a running Nextcloud+JSXC instance), code coverage as of d98186869 achieves a stunning 99%. 
This is the output of nosetests3 in the top-level directory (with online tests, based on the above version).
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Name Stmts Miss Cover Missing
------------------------------------------------------
xclib/__init__.py 28 0 100%
xclib/auth.py 97 0 100%
xclib/authops.py 135 1 99% 116
xclib/check.py 8 0 100%
xclib/configuration.py 70 1 99% 152
xclib/db.py 132 1 99% 156
xclib/dbmops.py 19 0 100%
xclib/ejabberd_io.py 34 2 94% 33-34
xclib/ejabberdctl.py 31 0 100%
xclib/isuser.py 25 0 100%
xclib/postfix_io.py 25 0 100%
xclib/prosody_io.py 17 0 100%
xclib/roster.py 56 0 100%
xclib/roster_thread.py 88 0 100%
xclib/saslauthd_io.py 36 2 94% 35-36
xclib/sigcloud.py 49 1 98% 76
xclib/sockact.py 27 0 100%
xclib/utf8.py 18 0 100%
xclib/version.py 1 0 100%
------------------------------------------------------
TOTAL 896 8 99%
-----------------------------------------------------------------------------
100 tests run in 2.9 seconds.
2 skipped (98 tests passed)