completion: document tilde expansion failure in tests

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Felipe Contreras

t/t9902-completion.sh

@@ -415,4 +415,13 @@ test_expect_success 'complete files' '
 	test_completion "git add mom" "momified"
 '
 
+test_expect_failure 'complete with tilde expansion' '
+	git init tmp && cd tmp &&
+	test_when_finished "cd .. && rm -rf tmp" &&
+
+	touch ~/tmp/file &&
+
+	test_completion "git add ~/tmp/" "~/tmp/file"
+'
+
 test_done