This series of patches is to cover a case in fullcopytracing algorithms
where both the merging csets are not descendant of merge base.
In this algorithm we call a merging cset "dirty" if that cset is not the
descendant of merge base. That said, added test in this patch cover case
when both the merging csets are "dirty".
Actually this case of "both dirty" was encountered by Pulkit when he was
working on content-divergence where it is possible that both the csets
are not descendant of merging base.
For reference you can look into: https://phab.mercurial-scm.org/D3896
As this test run fine without any error and correctly traced the copies, I
added this test to make sure that it doesn't break even after I will modify
some code in next patches to fix an error. Next patch adds the tests where
this algorithm throws an error for the same case of "both dirty".
Since this does not seem to set experimental.copytrace = heuristics (right?), this is probably not the right file for the test case. I recently added test-copies.t, which may be a better place for this. That file doesn't yet have any tests for mergecopies() (only for pathcopies()), but I was probably going to add that later anyway. Depending on how many tests I would add, I might have put all mergecopies() tests in a separate file, but since there isn't much at this point (only these few that you're adding), it probably makes sense for them to live in test-copies.t.