It is possible to test AT commands passing the desidered command to void test_at(const char* command) function in main.
Do not forget to put "AT+" before the actual command and "\r\n" after the command.
The firmware gives the opportunity to send AT commands without embedding them in the code.
The shell is activated calling init_uart() function.
Once ready message is shown it is possible to write the AT command press enter to add /n/r chars then write the '@' char, this is the trigger that send the command to the modem.