$CFG->behat_dataroot, $CFG->behat_prefix and $CFG->behat_wwwroot values need to be different than $CFG->dataroot, $CFG->prefix, $CFG->wwwroot, $CFG->phpunit_dataroot and $CFG->phpunit_prefix values.<br/>Or, if $CFG->behat_prefix is the same, $CFG->behat_dbname or $CFG->behat_dbhost need to be different from $CFG->phpunit_dbname and $CFG->phpunit_dbhost and from $CFG->dbname and $CFG->dbhost.