patch 8.1.0986: rename() is not propertly tested

Problem:    rename() is not propertly tested.
Solution:   Add tests. (Dominique Pelle, closes #4061)
diff --git a/src/testdir/test_alot.vim b/src/testdir/test_alot.vim
index 204796a..47fe5be 100644
--- a/src/testdir/test_alot.vim
+++ b/src/testdir/test_alot.vim
@@ -48,6 +48,7 @@
 source test_put.vim
 source test_recover.vim
 source test_reltime.vim
+source test_rename.vim
 source test_scroll_opt.vim
 source test_searchpos.vim
 source test_set.vim