Why TestExplorer in VS2015 failed to load Pester module?
As I stated in my question: I added the folder with the Pester to the environment variable called PSModulePath, but I added to the end of it.
For some reason the adaptor looks for the path of module only under the first folder in that environment variable.
I changed the order and moved the path to the beginning of the string. Voila!! it works.