./darknet detector train ./cfg/voc.data ./cfg/yolov3-custom.cfg darknet53.conv.74
running in your guide using your test data

https://towardsdatascience.com/real-time-mask-detection-with-yolov3-21ae0a1724b4

darknet: ./src/parser.c:315: parse_yolo: Assertion `l.outputs == params.inputs' failed.
Aborted (core dumped)