func CheckRPCsToBackend(ctx context.Context, cc *grpc.ClientConn, wantAddr resolver.Address) error
CheckRPCsToBackend makes a bunch of RPCs on the given ClientConn and verifies if the RPCs are routed to a peer matching wantAddr.
Returns a non-nil error if context deadline expires before all RPCs begin to be routed to the peer matching wantAddr, or if the backend returns RPC errors.