improve main package test coverage

ref #241

stream.go

@@ -13,11 +13,6 @@ import (
 	"github.com/lucas-clemente/quic-go/utils"
 )
 
-var (
-	errFlowControlViolation           = qerr.FlowControlReceivedTooMuchData
-	errConnectionFlowControlViolation = qerr.FlowControlReceivedTooMuchData
-)
-
 // A Stream assembles the data from StreamFrames and provides a super-convenient Read-Interface
 //
 // Read() and Write() may be called concurrently, but multiple calls to Read() or Write() individually must be synchronized manually.
@@ -203,10 +198,10 @@ func (s *stream) AddStreamFrame(frame *frames.StreamFrame) error {
 	err := s.flowControlManager.UpdateHighestReceived(s.streamID, maxOffset)
 
 	if err == flowcontrol.ErrStreamFlowControlViolation {
-		return errFlowControlViolation
+		return qerr.FlowControlReceivedTooMuchData
 	}
 	if err == flowcontrol.ErrConnectionFlowControlViolation {
-		return errConnectionFlowControlViolation
+		return qerr.FlowControlReceivedTooMuchData
 	}
 	if err != nil {
 		return err