fix for non-deterministic test.

pkg/testsupport/channelreadwritecloser.go

@@ -51,7 +51,17 @@ func (rw *ChannelReadWriter) Write(p []byte) (n int, err error) {
 	if rw.closed {
 		return 0, errors.New("Write on closed channel")
 	}
+
+	// if context is canceled it should never write
 	select {
+	case <-rw.ctx.Done():
+		rw.Close()
+		return 0, io.ErrClosedPipe
+	default:
+	}
+
+	select {
+	// deal with closing duirng the write
 	case <-rw.ctx.Done():
 		rw.Close()
 		return 0, io.ErrClosedPipe

pkg/testsupport/inmemoryconnection.go

@@ -11,7 +11,8 @@ type InmemoryConnection struct {
 
 func NewInmemoryConnection(ctx context.Context, addr string) *InmemoryConnection {
 	pipe := InmemoryConnection{
-		ctx:         ctx,
+		ctx: ctx,
+		// arbitrary unbuffered channel, unbuffered is more similar to TCP connections.
 		frontToBack: make(chan []byte),
 		backToFront: make(chan []byte),
 		addr:        addr,

pkg/testsupport/inmemoryconnection_test.go

@@ -0,0 +1 @@
+package testsupport