How to concatenate strings
You cannot "add" character arrays like that. You may try to use a
String object instead, as these do support the + operator as a way
to concatenate them:

String message = (String(celcius) + " deg Celcius, "
               + relativeHumidity + " relative humidity");
const char *c_message = message.c_str();


And then you use c_message in place of your test variable.
Note that only the first element (celcius here) needs to be explicitly
converted to a String object. The other conversions happen implicitly.

Edit: Updated the code to avoid using the internal state of a
(possibly destroyed) temporary object.