Try changing this line:
$AuthNet_required[0][$nextIndex] = "x_test_request";
$AuthNet_required[1][$nextIndex] = "".($WA_Authorize_Net_API_Credentials_TestMode) ."";
to:
$AuthNet_required[0][$nextIndex] = "x_test_request";
$AuthNet_required[1][$nextIndex] = "false";