ESP32 Spi Slave

I am attempting to get the "An Example for Slave SPI Communication on ESP32 and Arduino Platform" from Github, GitHub - iPAS/esp32-slave-spi: An Example for Slave SPI Communication on ESP32 and Arduino Platform , operational.

However, I am getting 50 some errors when attempting to compile the "test.ino" code presented as an example on the github site. The errors are mostly "undefined reference" to variables in SimpleArray.h and one or two in SlaveSPI.h.

It would seem I'm missing a file, reference, or something and wondering if anyone could help me get this compiled and uploaded to my Esp32DevModule?

Many Thanks,