diff --git a/metrics/engine/engine_test.go b/metrics/engine/engine_test.go
index 43cb5e66dc02..06267cfa3c86 100644
--- a/metrics/engine/engine_test.go
+++ b/metrics/engine/engine_test.go
@@ -176,3 +176,306 @@ func newTestMetricsEngine(t *testing.T) MetricsEngine {
 func zeroTestRunDuration() time.Duration {
 	return 0
 }
+
+/*
+// FIXME: This test is too brittle,
+// move them as e2e tests and consider to simplify.
+//
+func TestSentReceivedMetrics(t *testing.T) {
+	t.Parallel()
+	tb := httpmultibin.NewHTTPMultiBin(t)
+	tr := tb.Replacer.Replace
+
+	type testScript struct {
+		Code                 string
+		NumRequests          int64
+		ExpectedDataSent     int64
+		ExpectedDataReceived int64
+	}
+	testScripts := []testScript{
+		{tr(`import http from "k6/http";
+			export default function() {
+				http.get("HTTPBIN_URL/bytes/15000");
+			}`), 1, 0, 15000},
+		// NOTE: This needs to be improved, in the case of HTTPS IN URL
+		// it's highly possible to meet the case when data received is out
+		// of in the possible interval
+		{tr(`import http from "k6/http";
+			export default function() {
+				http.get("HTTPBIN_URL/bytes/5000");
+				http.get("HTTPSBIN_URL/bytes/5000");
+				http.batch(["HTTPBIN_URL/bytes/10000", "HTTPBIN_URL/bytes/20000", "HTTPSBIN_URL/bytes/10000"]);
+			}`), 5, 0, 50000},
+		{tr(`import http from "k6/http";
+			let data = "0123456789".repeat(100);
+			export default function() {
+				http.post("HTTPBIN_URL/ip", {
+					file: http.file(data, "test.txt")
+				});
+			}`), 1, 1000, 100},
+		// NOTE(imiric): This needs to keep testing against /ws-echo-invalid because
+		// this test is highly sensitive to metric data, and slightly differing
+		// WS server implementations might introduce flakiness.
+		// See https://github.com/k6io/k6/pull/1149
+		{tr(`import ws from "k6/ws";
+			let data = "0123456789".repeat(100);
+			export default function() {
+				ws.connect("WSBIN_URL/ws-echo-invalid", null, function (socket) {
+					socket.on('open', function open() {
+						socket.send(data);
+					});
+					socket.on('message', function (message) {
+						socket.close();
+					});
+				});
+			}`), 2, 1000, 1000},
+	}
+
+	type testCase struct{ Iterations, VUs int64 }
+	testCases := []testCase{
+		{1, 1}, {2, 2}, {2, 1}, {5, 2}, {25, 2}, {50, 5},
+	}
+
+	runTest := func(t *testing.T, ts testScript, tc testCase, noConnReuse bool) (float64, float64) {
+		r, err := js.New(
+			getTestPreInitState(t),
+			&loader.SourceData{URL: &url.URL{Path: "/script.js"}, Data: []byte(ts.Code)},
+			nil,
+		)
+		require.NoError(t, err)
+
+		mockOutput := mockoutput.New()
+		test := newTestEngine(t, nil, r, []output.Output{mockOutput}, lib.Options{
+			Iterations:            null.IntFrom(tc.Iterations),
+			VUs:                   null.IntFrom(tc.VUs),
+			Hosts:                 types.NullHosts{Trie: tb.Dialer.Hosts, Valid: true},
+			InsecureSkipTLSVerify: null.BoolFrom(true),
+			NoVUConnectionReuse:   null.BoolFrom(noConnReuse),
+			Batch:                 null.IntFrom(20),
+		})
+
+		errC := make(chan error)
+		go func() { errC <- test.run() }()
+
+		select {
+		case <-time.After(10 * time.Second):
+			t.Fatal("Test timed out")
+		case err := <-errC:
+			require.NoError(t, err)
+		}
+		test.wait()
+
+		checkData := func(name string, expected int64) float64 {
+			data := getMetricSum(mockOutput, name)
+			expectedDataMin := float64(expected * tc.Iterations)
+			expectedDataMax := float64((expected + ts.NumRequests*expectedHeaderMaxLength) * tc.Iterations)
+
+			if data < expectedDataMin || data > expectedDataMax {
+				t.Errorf(
+					"The %s sum should be in the interval [%f, %f] but was %f",
+					name, expectedDataMin, expectedDataMax, data,
+				)
+			}
+			return data
+		}
+
+		return checkData(metrics.DataSentName, ts.ExpectedDataSent),
+			checkData(metrics.DataReceivedName, ts.ExpectedDataReceived)
+	}
+
+	getTestCase := func(t *testing.T, ts testScript, tc testCase) func(t *testing.T) {
+		return func(t *testing.T) {
+			t.Parallel()
+			noReuseSent, noReuseReceived := runTest(t, ts, tc, true)
+			reuseSent, reuseReceived := runTest(t, ts, tc, false)
+
+			if noReuseSent < reuseSent {
+				t.Errorf("reuseSent=%f is greater than noReuseSent=%f", reuseSent, noReuseSent)
+			}
+			if noReuseReceived < reuseReceived {
+				t.Errorf("reuseReceived=%f is greater than noReuseReceived=%f", reuseReceived, noReuseReceived)
+			}
+		}
+	}
+
+	// This Run will not return until the parallel subtests complete.
+	t.Run("group", func(t *testing.T) {
+		t.Parallel()
+		for tsNum, ts := range testScripts {
+			for tcNum, tc := range testCases {
+				t.Run(
+					fmt.Sprintf("SentReceivedMetrics_script[%d]_case[%d](%d,%d)", tsNum, tcNum, tc.Iterations, tc.VUs),
+					getTestCase(t, ts, tc),
+				)
+			}
+		}
+	})
+}
+
+func TestEmittedMetricsWhenScalingDown(t *testing.T) {
+	t.Parallel()
+	tb := httpmultibin.NewHTTPMultiBin(t)
+
+	script := []byte(tb.Replacer.Replace(`
+		import http from "k6/http";
+		import { sleep } from "k6";
+
+		export let options = {
+			systemTags: ["iter", "vu", "url"],
+			scenarios: {
+				we_need_hard_stop_and_ramp_down: {
+					executor: "ramping-vus",
+					// Start with 2 VUs for 4 seconds and then quickly scale down to 1 for the next 4s and then quit
+					startVUs: 2,
+					stages: [
+						{ duration: "4s", target: 2 },
+						{ duration: "0s", target: 1 },
+						{ duration: "4s", target: 1 },
+					],
+					gracefulStop: "0s",
+					gracefulRampDown: "0s",
+				},
+			},
+		};
+
+		export default function () {
+			console.log("VU " + __VU + " starting iteration #" + __ITER);
+			http.get("HTTPBIN_IP_URL/bytes/15000");
+			sleep(3.1);
+			http.get("HTTPBIN_IP_URL/bytes/15000");
+			console.log("VU " + __VU + " ending iteration #" + __ITER);
+		};
+	`))
+
+	runner, err := js.New(
+		getTestPreInitState(t),
+		&loader.SourceData{URL: &url.URL{Path: "/script.js"}, Data: script},
+		nil,
+	)
+	require.NoError(t, err)
+
+	mockOutput := mockoutput.New()
+	test := newTestEngine(t, nil, runner, []output.Output{mockOutput}, lib.Options{})
+
+	errC := make(chan error)
+	go func() { errC <- test.run() }()
+
+	select {
+	case <-time.After(12 * time.Second):
+		t.Fatal("Test timed out")
+	case err := <-errC:
+		require.NoError(t, err)
+		test.wait()
+		require.False(t, test.engine.IsTainted())
+	}
+
+	// The 3.1 sleep in the default function would cause the first VU to complete 2 full iterations
+	// and stat executing its third one, while the second VU will only fully complete 1 iteration
+	// and will be canceled in the middle of its second one.
+	assert.Equal(t, 3.0, getMetricSum(mockOutput, metrics.IterationsName))
+
+	// That means that we expect to see 8 HTTP requests in total, 3*2=6 from the complete iterations
+	// and one each from the two iterations that would be canceled in the middle of their execution
+	assert.Equal(t, 8.0, getMetricSum(mockOutput, metrics.HTTPReqsName))
+
+	// And we expect to see the data_received for all 8 of those requests. Previously, the data for
+	// the 8th request (the 3rd one in the first VU before the test ends) was cut off by the engine
+	// because it was emitted after the test officially ended. But that was mostly an unintended
+	// consequence of the fact that those metrics were emitted only after an iteration ended when
+	// it was interrupted.
+	dataReceivedExpectedMin := 15000.0 * 8
+	dataReceivedExpectedMax := (15000.0 + expectedHeaderMaxLength) * 8
+	dataReceivedActual := getMetricSum(mockOutput, metrics.DataReceivedName)
+	if dataReceivedActual < dataReceivedExpectedMin || dataReceivedActual > dataReceivedExpectedMax {
+		t.Errorf(
+			"The data_received sum should be in the interval [%f, %f] but was %f",
+			dataReceivedExpectedMin, dataReceivedExpectedMax, dataReceivedActual,
+		)
+	}
+
+	// Also, the interrupted iterations shouldn't affect the average iteration_duration in any way, only
+	// complete iterations should be taken into account
+	durationCount := float64(getMetricCount(mockOutput, metrics.IterationDurationName))
+	assert.Equal(t, 3.0, durationCount)
+	durationSum := getMetricSum(mockOutput, metrics.IterationDurationName)
+	assert.InDelta(t, 3.35, durationSum/(1000*durationCount), 0.25)
+}
+
+func TestMetricsEmission(t *testing.T) {
+	if !isWindows {
+		t.Parallel()
+	}
+
+	testCases := []struct {
+		method             string
+		minIterDuration    string
+		defaultBody        string
+		expCount, expIters float64
+	}{
+		// Since emission of Iterations happens before the minIterationDuration
+		// sleep is done, we expect to receive metrics for all executions of
+		// the `default` function, despite of the lower overall duration setting.
+		{"minIterationDuration", `"300ms"`, "testCounter.add(1);", 16.0, 16.0},
+		// With the manual sleep method and no minIterationDuration, the last
+		// `default` execution will be cutoff by the duration setting, so only
+		// 3 sets of metrics are expected.
+		{"sleepBeforeCounterAdd", "null", "sleep(0.3); testCounter.add(1); ", 12.0, 12.0},
+		// The counter should be sent, but the last iteration will be incomplete
+		{"sleepAfterCounterAdd", "null", "testCounter.add(1); sleep(0.3); ", 16.0, 12.0},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.method, func(t *testing.T) {
+			if !isWindows {
+				t.Parallel()
+			}
+			runner, err := js.New(
+				getTestPreInitState(t),
+				&loader.SourceData{URL: &url.URL{Path: "/script.js"}, Data: []byte(fmt.Sprintf(`
+				import { sleep } from "k6";
+				import { Counter } from "k6/metrics";
+
+				let testCounter = new Counter("testcounter");
+
+				export let options = {
+					scenarios: {
+						we_need_hard_stop: {
+							executor: "constant-vus",
+							vus: 4,
+							duration: "1s",
+							gracefulStop: "0s",
+						},
+					},
+					minIterationDuration: %s,
+				};
+
+				export default function() {
+					%s
+				}
+				`, tc.minIterDuration, tc.defaultBody))},
+				nil,
+			)
+			require.NoError(t, err)
+
+			mockOutput := mockoutput.New()
+			test := newTestEngine(t, nil, runner, []output.Output{mockOutput}, runner.GetOptions())
+
+			errC := make(chan error)
+			go func() { errC <- test.run() }()
+
+			select {
+			case <-time.After(10 * time.Second):
+				t.Fatal("Test timed out")
+			case err := <-errC:
+				require.NoError(t, err)
+				test.wait()
+				require.False(t, test.engine.IsTainted())
+			}
+
+			assert.Equal(t, tc.expIters, getMetricSum(mockOutput, metrics.IterationsName))
+			assert.Equal(t, tc.expCount, getMetricSum(mockOutput, "testcounter"))
+		})
+	}
+}
+*/