How to perform usability testing if you are not the UX Expert?

Still thinking that usability testing is:

• the area of responsibility only for an experienced UX expert;
• work for the whole laboratory;
• long, expensive and extremely resourceful;
• difficult and unclear where to begin with? 

I will tell you how an ordinary engineer without deep expertise in UX can conduct usability testing. How to enforce your results with arguments and not be subjective using "easy/not easy".