implement a RTTGenerator for generating random RTTs for the UDP Proxy

ref #233

integrationtests/proxy/rtt_generator_test.go

@@ -0,0 +1,56 @@
+package proxy
+
+import (
+	"time"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("RTT settings", func() {
+	Context("no variance", func() {
+		It("always gets the same value", func() {
+			rttGen := newRttGenerator(10*time.Millisecond, 10*time.Millisecond)
+			for i := 0; i < 100; i++ {
+				Expect(rttGen.getRTT()).To(Equal(10 * time.Millisecond))
+			}
+		})
+	})
+
+	Context("random RTT", func() {
+		var rttGen rttGenerator
+
+		BeforeEach(func() {
+			rttGen = newRttGenerator(10*time.Millisecond, 30*time.Millisecond)
+		})
+
+		It("has the right mean value", func() {
+			var rttSum time.Duration
+			rep := 1000
+			for i := 0; i < rep; i++ {
+				rttSum += rttGen.getRTT()
+			}
+			averageRTT := rttSum.Nanoseconds() / 1000 / int64(rep) // in microseconds
+			Expect(averageRTT).To(BeNumerically("~", 20000, 1000)) // between 19 and 21 microseconds
+		})
+
+		It("covers the whole interval", func() {
+			var max time.Duration
+			min := time.Hour
+
+			rep := 1000
+			for i := 0; i < rep; i++ {
+				rtt := rttGen.getRTT()
+				if rtt > max {
+					max = rtt
+				}
+				if rtt < min {
+					min = rtt
+				}
+			}
+
+			Expect(min.Nanoseconds() / 1000).To(BeNumerically("<", 11000))
+			Expect(max.Nanoseconds() / 1000).To(BeNumerically(">", 29000))
+		})
+	})
+})