patch 8.2.0023: command line editing not sufficiently tested

Problem:    Command line editing not sufficiently tested.
Solution:   Add more tests. (Dominique Pelle, closes #5374)
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index db6b4fa..fab1460 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -97,6 +97,7 @@
 	test_ex_equal \
 	test_ex_undo \
 	test_ex_z \
+	test_ex_mode \
 	test_excmd \
 	test_exec_while_if \
 	test_execute_func \