[test/font] Start adding tests for hb-font.h

test/test-unicode.c

diff --git a/test/test-unicode.c b/test/test-unicode.c
index 2e15e95..e163aba 100644
--- a/test/test-unicode.c
+++ b/test/test-unicode.c
@@ -555,6 +555,7 @@
 {
   hb_unicode_funcs_t *uf = hb_unicode_funcs_get_empty ();
 
+  g_assert (uf);
   g_assert (hb_unicode_funcs_is_immutable (uf));
   _test_unicode_properties_nil (uf);
 }