I'm spanking new to Blender (as in < 1 day), so this may be a false alarm, but a simple object with Fresnel/ColorMap/Toon BSDF is rendering black with Eevee. Even the Cycles render doesn't look right (or consistent, it gave different results when I tried it twice).
Build: Blender 2.8 beta (a38205fbd801 of 2019-03-14) Platform: Linux (Fedora 29) My model: https://www.dropbox.com/s/r58thvhxy58uq0k/Toon.blend?dl=1
BTW, I'm very impressed with the first few hours of playing with Blender 2.8. I am a Lightwave user looking to switch and have been checking out Maya, which looked really consistent and intuitive, when I heard of Blender 2.8 and its new design...and I must say so far it looks even more consistent and intuitive.