Well, there is the book "Ray Tracing from the Ground Up" [1], which although a bit outdated (stemming from 2007), gives in-depth discussions on many of the topics. The author discusses possible pitfalls on the way as well. There are a few chapters, which are still math-heavy (the ones discussing the principles of stochastic ray tracing, a.k.a. Monte Carlo ray tracing).

A helpful resource for me, personally, was the educational ray tracer "Nori" [2], which came with 5 assignments covering fundamentals of a ray-tracing system (intersection acceleration, Monte Carlo sampling, basic and advanced integrators, BRDFs, even microfacet material models). Assignments gave hints on how to integrate those features in the ray tracer, plus they provided ways to validate ray-traced results. Currently, the assignments are removed from the Nori's website, but one can find them using the Wayback Machine.

[1] "Ray Tracing from the Ground Up", by Kevin Suffern, September 2007, http://www.raytracegroundup.com/

[2] Nori: an educational ray tracer, Dr. Wenzel Jakob, https://wjakob.github.io/nori/# (using Wayback machine to access assignments https://web.archive.org/web/20200110040505/https://wjakob.gi...)