Improve rate limiter tests

Co-authored-by: Julien Salleyron <julien.salleyron@gmail.com>

pkg/middlewares/ratelimiter/rate_limiter_test.go

@@ -75,7 +75,9 @@ func TestRateLimit(t *testing.T) {
 	testCases := []struct {
 		desc         string
 		config       dynamic.RateLimit
-		reqCount int
+		loadDuration time.Duration
+		incomingLoad int // in reqs/s
+		burst        int
 	}{
 		{
 			desc: "Average is respected",
@@ -83,15 +85,47 @@ func TestRateLimit(t *testing.T) {
 				Average: 100,
 				Burst:   1,
 			},
-			reqCount: 200,
+			loadDuration: 2 * time.Second,
+			incomingLoad: 400,
 		},
 		{
-			desc: "Burst is taken into account",
+			desc: "burst allowed, no bursty traffic",
+			config: dynamic.RateLimit{
+				Average: 100,
+				Burst:   100,
+			},
+			loadDuration: 2 * time.Second,
+			incomingLoad: 200,
+		},
+		{
+			desc: "burst allowed, initial burst, under capacity",
+			config: dynamic.RateLimit{
+				Average: 100,
+				Burst:   100,
+			},
+			loadDuration: 2 * time.Second,
+			incomingLoad: 200,
+			burst:        50,
+		},
+		{
+			desc: "burst allowed, initial burst, over capacity",
+			config: dynamic.RateLimit{
+				Average: 100,
+				Burst:   100,
+			},
+			loadDuration: 2 * time.Second,
+			incomingLoad: 200,
+			burst:        150,
+		},
+		{
+			desc: "burst over average, initial burst, over capacity",
 			config: dynamic.RateLimit{
 				Average: 100,
 				Burst:   200,
 			},
-			reqCount: 300,
+			loadDuration: 2 * time.Second,
+			incomingLoad: 200,
+			burst:        300,
 		},
 		{
 			desc: "Zero average ==> no rate limiting",
@@ -99,26 +133,32 @@ func TestRateLimit(t *testing.T) {
 				Average: 0,
 				Burst:   1,
 			},
-			reqCount: 100,
+			incomingLoad: 1000,
+			loadDuration: time.Second,
 		},
 	}
 
 	for _, test := range testCases {
 		test := test
 		t.Run(test.desc, func(t *testing.T) {
+
 			t.Parallel()
 
 			reqCount := 0
+			dropped := 0
 			next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 				reqCount++
 			})
-
 			h, err := New(context.Background(), next, test.config, "rate-limiter")
 			require.NoError(t, err)
 
+			period := time.Duration(1e9 / test.incomingLoad)
 			start := time.Now()
+			end := start.Add(test.loadDuration)
+			ticker := time.NewTicker(period)
+			defer ticker.Stop()
 			for {
-				if reqCount >= test.reqCount {
+				if time.Now().After(end) {
 					break
 				}
 
@@ -127,34 +167,45 @@ func TestRateLimit(t *testing.T) {
 				w := httptest.NewRecorder()
 
 				h.ServeHTTP(w, req)
-				// TODO(mpl): predict and count the 200 VS the 429?
+				if w.Result().StatusCode != http.StatusOK {
+					dropped++
+				}
+				if test.burst > 0 && reqCount < test.burst {
+					// if a burst is defined we first hammer the server with test.burst requests as fast as possible
+					continue
+				}
+				<-ticker.C
 			}
-
 			stop := time.Now()
 			elapsed := stop.Sub(start)
+
 			if test.config.Average == 0 {
-				if elapsed > time.Millisecond {
-					t.Fatalf("rate should not have been limited, but: %d requests in %v", reqCount, elapsed)
+				if reqCount < 75*test.incomingLoad/100 {
+					t.Fatalf("we (arbitrarily) expect at least 75%% of the requests to go through with no rate limiting, and yet only %d/%d went through", reqCount, test.incomingLoad)
+				}
+				if dropped != 0 {
+					t.Fatalf("no request should have been dropped if rate limiting is disabled, and yet %d were", dropped)
 				}
 				return
 			}
 
-			// Assume allowed burst is initially consumed in an infinitesimal period of time
-			var expectedDuration time.Duration
-			if test.config.Average != 0 {
-				expectedDuration = time.Duration((int64(test.reqCount)-test.config.Burst+1)/test.config.Average) * time.Second
-			}
-
+			// Note that even when there is no bursty traffic,
+			// we take into account the configured burst,
+			// because it also helps absorbing non-bursty traffic.
+			wantCount := int(test.config.Average*int64(test.loadDuration/time.Second) + test.config.Burst)
 			// Allow for a 2% leeway
-			minDuration := expectedDuration * 98 / 100
-			maxDuration := expectedDuration * 102 / 100
-
-			if elapsed < minDuration {
-				t.Fatalf("rate was faster than expected: %d requests in %v", reqCount, elapsed)
-			}
-			if elapsed > maxDuration {
+			maxCount := wantCount * 102 / 100
+			// With very high CPU loads,
+			// we can expect some extra delay in addition to the rate limiting we already do,
+			// so we allow for some extra leeway there.
+			// Feel free to adjust wrt to the load on e.g. the CI.
+			minCount := wantCount * 95 / 100
+			if reqCount < minCount {
 				t.Fatalf("rate was slower than expected: %d requests in %v", reqCount, elapsed)
 			}
+			if reqCount > maxCount {
+				t.Fatalf("rate was faster than expected: %d requests in %v", reqCount, elapsed)
+			}
 		})
 	}
 }