tests: show IMM is broken when merging file empty in destination
When we are doing in-memory merging, and we are merging a file which is empty in
merge destination, it leads to error 'abort: xxx not found in manifest'.
Next patch will fix this error.
Differential Revision: https://phab.mercurial-scm.org/D6307
#require docutils gettext
$ $TESTDIR/check-gendoc da
checking for parse errors