# Functions
CheckPropagatesErrorClient - NetworkServiceClient that will check to see if the clientUnderTest correctly propagates error.
CheckPropogatesErrorServer - NetworkServiceServer that will check to see if the serverUnderTest correctly propagates error.
NewClient - returns NetworkServiceClient chain element that checks for an error being returned from the next element in the chain
t - *testing.T for checking isNil - if true, check that error is nil, if false, check that err is not nil.
NewServer - returns NetworkServiceServer chain element that checks for an error being returned from the next element in the chain
t - *testing.T for checking isNil - if true, check that error is nil, if false, check that err is not nil.