Restoring database always throwing exception
If you want to restore a *.bak file onto a machine e.g. TESTSERVER, then that *.bak file needs to be 


on a local drive of TESTSERVER, or:
on a share in the network that TESTSERVER can reach (a "public" share)


So if you have the *.bak file on your local PC MyPC, you can try to do a restore from \\MyPC\C$\ShareFolder\Backupfile.bak and this might or might not work. 

But you cannot use C:\ShareFolder\Backupfile.bak since that will go to the server's C:\ drive and look for that file - and thus you get the error message and it cannot be found.

After all: your SQL Server instance is running on TESTSERVER - so if that process there executes a restore from the C:\ drive, that'll be the C:\ drive on that server machine - not your local PC! If that server process on TESTSERVER can reach your machine, then you might use the UNC path notation to your local disk - so that might work.