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_syntax.vim b/src/testdir/test_syntax.vim
index ffa8e90..c0be4a0 100644
--- a/src/testdir/test_syntax.vim
+++ b/src/testdir/test_syntax.vim
@@ -119,6 +119,15 @@
   bd
 endfunc
 
+func Test_syntime_completion()
+  if !has('profile')
+    return
+  endif
+
+  call feedkeys(":syntime \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"syntime clear off on report', @:)
+endfunc
+
 func Test_syntax_list()
   syntax on
   let a = execute('syntax list')