Request failed: Exception occurred: Could not load file or assembly

Problem: 

When we add any web test plug in or web request plug in we are getting  error “Request failed: Exception occurred: Could not load file or assembly '<<Solution name>>, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.” 

Solution : We have to add your .CS file or folder contains file in deployment directory. 

Solution items --> Local.test settings --> Deployment --> Enable deployment (check box) and then add file / directory --> Save test settings.