PlainDocument doc = new PlainDocument();
doc.insertString(0, "cdefgh", null);
Position s = doc.createPosition(1);
harness.check(s.getOffset(), 1);
doc.insertString(0, "a", null);
harness.check(s.getOffset(), 2);
Position a = doc.createPosition(1);
harness.check(a.getOffset(), 1);
doc.insertString(1, "b", null);