fix racy session unit test

session_test.go

@@ -1055,13 +1055,16 @@ var _ = Describe("Session", func() {
 
 		It("sends ACK only packets", func() {
 			sph := mockackhandler.NewMockSentPacketHandler(mockCtrl)
+			sph.EXPECT().TimeUntilSend().AnyTimes()
 			sph.EXPECT().GetLossDetectionTimeout().AnyTimes()
 			sph.EXPECT().SendMode().Return(ackhandler.SendAck)
 			sph.EXPECT().ShouldSendNumPackets().Return(1000)
-			packer.EXPECT().MaybePackAckPacket(false)
-			runSession()
+			done := make(chan struct{})
+			packer.EXPECT().MaybePackAckPacket(false).Do(func(bool) { close(done) })
 			sess.sentPacketHandler = sph
-			Expect(sess.sendPackets()).To(Succeed())
+			runSession()
+			sess.scheduleSending()
+			Eventually(done).Should(BeClosed())
 		})
 
 		It("adds a BLOCKED frame when it is connection-level flow control blocked", func() {