tests: compile/observable: add missing checks

Signed-off-by: Philippe Gerum <rpm@xenomai.org>

tests/compile-tests/observable.cc

@@ -8,8 +8,14 @@
 
 int main(int argc, char *argv[])
 {
+	struct evl_notification nf;
+	struct evl_notice no;
+	int efd;
+
 	evl_new_observable("test");
-	evl_create_observable(EVL_CLONE_PRIVATE, "test");
+	efd = evl_create_observable(EVL_CLONE_PRIVATE, "test");
+	evl_update_observable(efd, &no, 1);
+	evl_read_observable(efd, &nf, 1);
 
 	return 0;
 }