patch 8.1.0559: command line completion not sufficiently tested

Problem:    Command line completion not sufficiently tested.
Solution:   Add more tests. (Dominique Pelle, closes #3622)
diff --git a/src/testdir/test_history.vim b/src/testdir/test_history.vim
index ca31e3f..16aad98 100644
--- a/src/testdir/test_history.vim
+++ b/src/testdir/test_history.vim
@@ -104,3 +104,8 @@
   call assert_equal('a', @/)
   bwipe!
 endfunc
+
+function Test_history_completion()
+  call feedkeys(":history \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"history / : = > ? @ all cmd debug expr input search', @:)
+endfunc