// heads
errorCollector.assertEquals(new RevisionSet(nodes5), complete.heads(parentHelper));
Nodeid[] nodes6 = { allRevs[9], allRevs[8] };
RevisionSet toR7 = complete.subtract(new RevisionSet(nodes6));
Nodeid[] nodes7 = { allRevs[7], allRevs[6], allRevs[4] };
errorCollector.assertEquals(new RevisionSet(nodes7), toR7.heads(parentHelper));
Nodeid[] nodes8 = { allRevs[5], allRevs[7] };
RevisionSet withoutNoMergeBranch = toR7.subtract(new RevisionSet(nodes8));
Nodeid[] nodes9 = { allRevs[6], allRevs[4] };
errorCollector.assertEquals(new RevisionSet(nodes9), withoutNoMergeBranch.heads(parentHelper));
errorCollector.assertEquals(complete.heads(parentHelper), complete.heads(parentHelper).heads(parentHelper));