patch 8.1.0389: :behave command is not tested

Problem:    :behave command is not tested.
Solution:   Add a test. (Dominique Pelle, closes #3429)
diff --git a/src/testdir/test_alot.vim b/src/testdir/test_alot.vim
index 7d300a4..ea829e0 100644
--- a/src/testdir/test_alot.vim
+++ b/src/testdir/test_alot.vim
@@ -3,6 +3,7 @@
 
 source test_assign.vim
 source test_backup.vim
+source test_behave.vim
 source test_bufline.vim
 source test_cd.vim
 source test_changedtick.vim