I am using graph to retrieve a list of filenames from a folder, however I am not able to mock the calls correctly in the unit test

Question

here is my code:

var uploadSession = await graphServiceClient.Drives[driveId]        
.Items["root"]
.ItemWithPath(fileName)
.CreateUploadSession
.PostAsync(uploadSessionRequestBody);  

the above code works, but I am not able to mock the call properly to make my tests pass. 
when calling ItemWithPath I get an Exception:

Invalid URI: The hostname could not be parsed. 

this exception happens deep in the graph code and I have no clue how to mock these tests.    rootRequestBuilder.ToGetRequestInformation().URI.OriginalString is not a valid parameter for newUriBuilder(parameter) in the test environment.