Test Framework uses the following code to collect logs when tests fail:

gather_logs () {
    # ...

    local archive=$LOGDIR/${TESTSUITE}-$ts.tar.bz2
    tar -jcf $archive $LOGDIR/*$ts* $LOGDIR/*${TESTSUITE}*

    # ...
}

Note that the names of the archives begin with $TESTSUITE, which means, if there are multiple failures in the same suite, then the archive of each such failure will contain all the prior archives.

In real world, I've encountered a test log directory with an over 6 GB size, thanks to those Russian doll tarballs. The test results couldn't be uploaded to Maloo, probably because of the huge size.