This repo contains the Arduino sketches that I used for a range test using a pair of ESP-01 running ESP-Now protocols.
The codes works on any ESP8266 modules, but it is not compatible with ESP-32 because ESP-32's implementation for ESP-Now has slightly different APIs.
For more details of the range test, please watch this YouTube video.
For more details dicsussion on the setup and the use of the sketches, it is covered in my blog.