Antenna connectivity test
This totally depends what the definitions are for a valid connection. I assume you are talking about data transmission by IEEE 802.11 (used by WiFi)? Then a MCU alone wouldn't be enough. You would require some kind of WiFi module and hook that up to the antenna. Then check if you receive data to be exactly the same, as the data that was sent by the transmitter. Whatever the transmitter may be: router, notebook, smartphone...

Edit:
If you would still go about charging its capacitance, I would consider the RC time, and use a comparator to see how long it takes for the comparator to output a high(er than) signal using the MCU. The comparator will likely never output higher than upper rail voltage. So connect - of comparator to reference voltage, + to the antenna as being the capacitor and output of comparator to MCU digital in or so.