add method to FlowControlManager to tell if Stream contribues to connection-level flow control

flowcontrol/flow_control_manager_test.go

@@ -171,5 +171,26 @@ var _ = Describe("Flow Control Manager", func() {
 				Expect(size).To(Equal(protocol.ByteCount(0x1000)))
 			})
 		})
+
+		Context("streams contributing to connection-level flow control", func() {
+			It("says that a stream contributes", func() {
+				fcm.NewStream(5, true)
+				contributes, err := fcm.StreamContributesToConnectionFlowControl(5)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(contributes).To(BeTrue())
+			})
+
+			It("says that a stream doesn't contribute", func() {
+				fcm.NewStream(3, false)
+				contributes, err := fcm.StreamContributesToConnectionFlowControl(3)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(contributes).To(BeFalse())
+			})
+
+			It("returns an error for an unknown stream", func() {
+				_, err := fcm.StreamContributesToConnectionFlowControl(1337)
+				Expect(err).To(HaveOccurred())
+			})
+		})
 	})
 })