Matthieu Prat [off-list ref] writes:
A test was designed for "git diff-index --cached -M" but the command is
run without the "-M" option (which makes the test essentially identical
to its preceding counterpart).
Very true and it seems that it has been that way from the day these
trio of tests were introduced by d7c9bf22 (diffcore-rename: don't
consider unmerged path as source, 2011-03-23).
Thanks for a fix. Will queue.