docs: def gc(ctx):
      """Runs housekeeping tasks to free up space.
  
      For now, this only removes saved but unused (unreachable) test results.
      """
      vcs = ctx.obj['vcs']
      count = 0
      with locking.lock(vcs, locking.Lock.tests_history):
          known_signatures = set(get_committed_signatures(vcs) + get_staged_signatures(vcs))
          for signature in get_signatures_with_results(vcs):
              if signature not in known_signatures:
                  count += 1
                  remove_results(vcs, signature)
      click.echo('Removed {} saved results.'.format(count))