patch 8.2.0385: menu functionality insufficiently tested

Problem:    Menu functionality insufficiently tested.
Solution:   Add tests.  Add menu_info(). (Yegappan Lakshmanan, closes #5760)
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index 5922efa..fdc009f 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -851,6 +851,12 @@
   CheckScreendump
   CheckFeature menu
 
+  menu Test.Foo Foo
+  call assert_fails('popup Test.Foo', 'E336:')
+  call assert_fails('popup Test.Foo.X', 'E327:')
+  call assert_fails('popup Foo', 'E337:')
+  unmenu Test.Foo
+
   let lines =<< trim END
 	one two three four five
 	and one two Xthree four five