How is BRDF usually implemented?

I have a small path tracer, and I am trying to figure out how to implement some basic BRDFs. Here's a brief description of the pipeline I use (without recursion):

1) For each pixel:
   1.1) For each sample:
      1.1.1) I construct a path.
      1.1.2) I calculate the contribution of this path.
      1.1.3) I calculate the "probability" of this path.
      1.1.4) Finally, I calculate the overall color value(taking into account number of samples, "probability" and contribution of the path).
   1.2) Take the sum of all samples' values and write it to the pixel.

So, I calculate the direction of reflected rays in the step 1.1.1) I construct a path. For now, I have implemented diffuse reflection, specular reflection, glossy reflection, refraction. Now I want to implement a complex BRDF, let's say Cook-Torrance BRDF. I see that it contains several components (diffuse reflection and specular reflection). How should I trace these rays to get the combination? Should I choose between diffuse_ray/specular_ray randomly and then accumulate the values as usual?(like, if a random value is more than 0.5 then I trace a diffuse ray, otherwise - specular) Or should I trace multiple rays from each intersection?

How is it usually implemented in physically-based renderers?

P.S. If somebody knows some good articles on this topic I would be glad to see them. I tried to read pbrt but it seems very complex and huge for me. And some things there are implemented differently, like the camera model and other stuff.