I don't see that `run(back_to_front)` will return a truthy value.  Please refer to [Scm::Adapters::AbstractAdapter](https://github.com/blackducksw/ohloh_scm/blob/master/lib/scm/adapters/abstract/system.rb#L18).  This calls `Shellout#run`, which calls `Shellout.execute`, which returns an array of `[status, outbuf.string, errbuf.string]`

It would be very helpful to have test coverage of this next_revision_xml method with the different pathways covered.