This issue pertains to bigtop-test-framework, not bigtop-tests.
When running the package tests, specifically upgrade tests, on debian platforms, doing "env DEBIAN_FRONTEND=noninteractive apt-get -y install $
" is not enough. dpkg will prompt you as to what to do about conf files that have been modified, and the tests will fail because they don't respond to the prompts.
According to http://raphaelhertzog.com/2010/09/21/debian-conffile-configuration-file-managed-by-dpkg/, you can use --force-conf* options; in particular
--force-confold: do not modify the current configuration file, the new version is installed with a .dpkg-dist suffix. With this option alone, even configuration files that you have not modified are left untouched. You need to combine it with --force-confdef to let dpkg overwrite configuration files that you have not modified.