I\'m using Path.Combine like so:
Path.Combine(\"test1/test2\", \"test3\\\\test4\");
The output I get is:
test1/test2\\test3\\te
Try using
var fullname = new DirectoryInfo(Path.Combine("f:/","test1/test2", "test3\\test4")).FullName;
This will result in
f:\test1\test2\test3\test4