Frontend unit tests cover durations, colours, statistics and health (closes #21)

New table-driven tests in test/unit/main.test.js: humanDuration, the
figure and sparkline colours either side of each latency boundary, a
target's min, max, average and median over an empty history, an
all-unreachable one, a mixed one, one of only answers and one whose
answers have different numbers of digits, and the four health states
either side of their thresholds, with targets found unreachable counted
as timed out. src/main.js exports the four names they need.

package.json gains a test script, which script/frontend-test runs with
the dot reporter and, if a test fails, again with the spec reporter
before failing. NODE_OPTIONS picks the reporter, since yarn appends its
arguments after the test files.

Model: opus-5-5

README.md

@@ -47,15 +47,17 @@ halves, so the root `make check` fails if either one is broken. We provide:
 - `script/setup` — make a fresh clone ready for development: bootstrap plus the
   git pre-commit hook
 - `script/projectname` — print the project name (used for the Docker image tag)
-- `script/test` — run `script/frontend-test`, then the backend's Go tests, each
-  under its own 30-second timeout
+- `script/test` — run `script/frontend-test`, then `backend/script/test`, the
+  backend's Go tests with the race detector and coverage
 - `script/lint` — run eslint, then golangci-lint, both in Docker, by building
   the `frontend-lint` and `lint` stages of `Dockerfile` without the cache
 - `script/fmt` — format all files (writes): prettier, then gofmt over `backend/`
 - `script/fmt-check` — check formatting (read-only): prettier, then gofmt
 - `script/check` — run test, lint, and fmt-check
 - `script/frontend-test` — run the unit tests in `test/unit/` with Node's
-  built-in test runner, then the production build
+  built-in test runner, through the `test` script in `package.json`, and if any
+  fails, run them again listing every test, and fail; then the production build.
+  Each run has a 30-second timeout
 - `script/frontend-lint` — run eslint with the rules in `eslint.config.js`; it
   runs inside the `frontend-lint` stage of `Dockerfile`, which `make lint`
   builds
@@ -267,7 +269,6 @@ properties.
 
 ## TODO
 
-- Add unit tests
 - Add configurable host list (environment variable or config file)
 - Add latency history export (CSV/JSON)
 - Add notification/alert when status changes to DEGRADED

TODO.md

@@ -23,6 +23,28 @@ latest run passes.
 
 # Completed Steps
 
+- 2026-10-03: the frontend's unit tests cover what the page computes (issue
+  #21): `humanDuration`, the latency colours of a figure and of a sparkline
+  either side of each boundary, a target's min, max, average and median latency
+  over an empty history, an all-unreachable one and a mixed one, and each of the
+  four health states either side of its thresholds. `package.json` has a `test`
+  script, so `yarn run test` and `npm run test` run them, and
+  `script/frontend-test` runs it: quietly, and if a test fails, again with every
+  test listed, and then fails. `src/main.js` now exports `humanDuration`,
+  `HostState`, `latencyClass` and `latencyHex` for the tests; nothing it does
+  changed
+- 2026-10-03: the backend's logs are one stream (issue #27): fx logs its own
+  steps of starting and stopping through the backend's logger, so off a terminal
+  every line the backend's own logger and fx write is JSON, where fx used to
+  write plain text to stderr. A config file that is found but cannot be read now
+  stops the start with its error, logged as JSON like a bad setting, where it
+  used to end in a Go panic. A test runs the server as a child process and
+  checks both. The backend logs its name, version and architecture once at
+  start. The health check's uptime keys are now `uptime_seconds` and
+  `uptime_human`; its path, content type, `"status":"ok"` and 200 are unchanged.
+  `SENTRY_DSN`, `METRICS_USERNAME` and `METRICS_PASSWORD` are still read and
+  still unused, and left out of `backend/README.md`, until issues #94 and #95
+  wire them up
 - 2026-10-03: the frontend has a real linter (issue #47, and item 2 of issue
   #28): `eslint` with its recommended rules, set in `eslint.config.js`, runs in
   a new `frontend-lint` stage of `Dockerfile`, which the frontend stage waits

backend/cmd/netwatch-server/main.go

@@ -16,6 +16,7 @@ import (
 	"sneak.berlin/go/netwatch/internal/server"
 
 	"go.uber.org/fx"
+	"go.uber.org/fx/fxevent"
 )
 
 //nolint:gochecknoglobals // set via ldflags at build time
@@ -62,6 +63,12 @@ func main() {
 	globals.Version = Version
 
 	fx.New(
+		// fx logs each step of starting and stopping through the
+		// server's own logger, so off a terminal those lines are
+		// JSON like every other line.
+		fx.WithLogger(func(log *logger.Logger) fxevent.Logger {
+			return &fxevent.SlogLogger{Logger: log.Get()}
+		}),
 		fx.Provide(
 			config.New,
 			globals.New,
@@ -72,6 +79,11 @@ func main() {
 			reportbuf.New,
 			server.New,
 		),
-		fx.Invoke(func(*server.Server) {}),
+		fx.Invoke(
+			// First, so the name and version are logged even when
+			// a setting stops the start.
+			func(log *logger.Logger) { log.Identify() },
+			func(*server.Server) {},
+		),
 	).Run()
 }

backend/cmd/netwatch-server/main_test.go

@@ -0,0 +1,227 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"os/signal"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"testing"
+	"time"
+)
+
+// The tests run main() in a child process, this test binary started
+// again with runMainEnv set, because main() can exit its process and
+// takes its settings from the environment.
+const runMainEnv = "NETWATCH_SERVER_RUN_MAIN"
+
+// childTimeout bounds each child's whole run; it is killed after it.
+const childTimeout = 10 * time.Second
+
+func TestMain(m *testing.M) {
+	if os.Getenv(runMainEnv) != "" {
+		// A SIGTERM that comes before fx catches it is dropped, not fatal.
+		signal.Notify(make(chan os.Signal, 1), syscall.SIGTERM)
+		main()
+
+		return
+	}
+
+	os.Exit(m.Run())
+}
+
+// TestOutputIsJSON: off a terminal, every line the server writes from
+// start to stop is JSON, fx's own lines included.
+func TestOutputIsJSON(t *testing.T) {
+	t.Parallel()
+
+	ctx, cancel := context.WithTimeout(t.Context(), childTimeout)
+	defer cancel()
+
+	port := freePort(ctx, t)
+	child, stdout, stderr := startServer(ctx, t, t.TempDir(), port)
+
+	waitForHealthcheck(ctx, t, port)
+
+	// The child drops a SIGTERM that comes before fx catches it (see
+	// TestMain), so send one every 100ms until the test ends. ctx
+	// bounds the wait: when it ends, the child is killed.
+	stop := make(chan struct{})
+	defer close(stop)
+
+	go func() {
+		for {
+			_ = child.Process.Signal(syscall.SIGTERM)
+
+			select {
+			case <-stop:
+				return
+			case <-time.After(100 * time.Millisecond):
+			}
+		}
+	}()
+
+	err := child.Wait()
+	if err != nil {
+		t.Fatalf("server exit = %v, want success", err)
+	}
+
+	requireJSONLines(t, stdout, stderr)
+
+	if !strings.Contains(stdout.String(), `"msg":"starting"`) {
+		t.Fatalf("no startup line in stdout:\n%s", stdout)
+	}
+}
+
+// TestMalformedConfigFileStopsTheStart: a config file the server finds
+// but cannot read stops the start, and the error is logged as JSON.
+func TestMalformedConfigFileStopsTheStart(t *testing.T) {
+	t.Parallel()
+
+	ctx, cancel := context.WithTimeout(t.Context(), childTimeout)
+	defer cancel()
+
+	home := t.TempDir()
+	dir := filepath.Join(home, ".config", "netwatch-server")
+
+	err := os.MkdirAll(dir, 0o750)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = os.WriteFile(filepath.Join(dir, "netwatch-server.yaml"),
+		[]byte("PORT: [8080\n"), 0o600)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	child, stdout, stderr := startServer(ctx, t, home, freePort(ctx, t))
+
+	err = child.Wait()
+	if child.ProcessState.ExitCode() != 1 {
+		t.Fatalf("server exit = %v, want exit status 1", err)
+	}
+
+	requireJSONLines(t, stdout, stderr)
+
+	if !strings.Contains(stdout.String(), "netwatch-server.yaml") {
+		t.Fatalf("no error naming the config file in stdout:\n%s", stdout)
+	}
+}
+
+// startServer runs main() in a child process listening on
+// 127.0.0.1:port, with home as its HOME and working directory and its
+// data directory in home, so it touches nothing outside home. Its
+// stdout and stderr go to the two buffers returned, which hold all of
+// it once child.Wait returns. The child is killed when ctx ends, and
+// killed and reaped when the test ends if nothing waited for it.
+func startServer(
+	ctx context.Context,
+	t *testing.T,
+	home, port string,
+) (*exec.Cmd, *bytes.Buffer, *bytes.Buffer) {
+	t.Helper()
+
+	self, err := os.Executable()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var stdout, stderr bytes.Buffer
+
+	child := exec.CommandContext(ctx, self) //nolint:gosec // this test binary
+	child.Dir = home
+	child.Env = append(os.Environ(),
+		runMainEnv+"=1",
+		"HOME="+home,
+		"DATA_DIR="+filepath.Join(home, "data"),
+		"BIND_ADDRESS=127.0.0.1",
+		"PORT="+port,
+	)
+	child.Stdout = &stdout
+	child.Stderr = &stderr
+
+	err = child.Start()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Cleanup(func() {
+		if child.ProcessState == nil {
+			_ = child.Process.Kill()
+			_ = child.Wait()
+		}
+	})
+
+	return child, &stdout, &stderr
+}
+
+// freePort returns a TCP port on 127.0.0.1 that was free a moment ago.
+func freePort(ctx context.Context, t *testing.T) string {
+	t.Helper()
+
+	var lc net.ListenConfig
+
+	l, err := lc.Listen(ctx, "tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_ = l.Close()
+
+	_, port, err := net.SplitHostPort(l.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return port
+}
+
+// waitForHealthcheck returns once the health check on port answers 200.
+func waitForHealthcheck(ctx context.Context, t *testing.T, port string) {
+	t.Helper()
+
+	url := "http://127.0.0.1:" + port + "/.well-known/healthcheck"
+
+	for {
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		resp, err := http.DefaultClient.Do(req)
+		if err == nil {
+			_ = resp.Body.Close()
+
+			if resp.StatusCode == http.StatusOK {
+				return
+			}
+		}
+
+		select {
+		case <-ctx.Done():
+			t.Fatalf("health check never answered: %v", err)
+		case <-time.After(50 * time.Millisecond):
+		}
+	}
+}
+
+// requireJSONLines fails the test on each line of outs that is not
+// JSON.
+func requireJSONLines(t *testing.T, outs ...*bytes.Buffer) {
+	t.Helper()
+
+	for _, out := range outs {
+		for line := range strings.Lines(out.String()) {
+			if !json.Valid([]byte(line)) {
+				t.Errorf("line is not JSON: %s", line)
+			}
+		}
+	}
+}

backend/internal/config/config.go

@@ -73,7 +73,8 @@ type Config struct {
 
 // New loads configuration from env, .env files, and config
 // files, returning a fully resolved Config. It fails, with an error
-// naming the setting, on a value the server cannot use.
+// naming the setting, on a value the server cannot use, and on a
+// config file it finds but cannot read.
 func New(
 	_ fx.Lifecycle,
 	params Params,
@@ -106,8 +107,8 @@ func New(
 	if err != nil {
 		var notFound viper.ConfigFileNotFoundError
 		if !errors.As(err, &notFound) {
-			log.Error("config file malformed", "error", err)
-			panic(err)
+			return nil, fmt.Errorf("config file %s: %w",
+				viper.ConfigFileUsed(), err)
 		}
 	}
 

backend/internal/handlers/healthcheck.go

@@ -6,6 +6,6 @@ import "net/http"
 // endpoint.
 func (s *Handlers) HandleHealthCheck() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		s.respondJSON(w, r, s.hc.Check(), http.StatusOK)
+		s.respondJSON(w, r, s.hc.Healthcheck(), http.StatusOK)
 	}
 }

backend/internal/handlers/healthcheck_test.go

@@ -50,8 +50,8 @@ func newStartedHandlers(t *testing.T, g *globals.Globals) *handlers.Handlers {
 
 // TestHandleHealthCheck checks the health check's answer: 200, a JSON
 // content type, and a JSON object with exactly the fields of
-// healthcheck.Response, carrying this server's name and version and
-// an uptime counted from its start.
+// healthcheck.HealthcheckResponse, carrying this server's name and
+// version and an uptime counted from its start.
 func TestHandleHealthCheck(t *testing.T) {
 	t.Parallel()
 
@@ -82,7 +82,7 @@ func TestHandleHealthCheck(t *testing.T) {
 	}
 
 	fields := []string{
-		"appname", "now", "status", "uptimeHuman", "uptimeSeconds", "version",
+		"appname", "now", "status", "uptime_human", "uptime_seconds", "version",
 	}
 	if got := slices.Sorted(maps.Keys(body)); !slices.Equal(got, fields) {
 		t.Fatalf("fields = %v, want %v", got, fields)
@@ -104,17 +104,17 @@ func TestHandleHealthCheck(t *testing.T) {
 	}
 
 	// Started just now, so the uptime is well under a minute.
-	human, _ := body["uptimeHuman"].(string)
+	human, _ := body["uptime_human"].(string)
 
 	uptime, err := time.ParseDuration(human)
 	if err != nil || uptime > time.Minute {
-		t.Errorf("uptimeHuman = %q, want a duration under a minute (%v)",
+		t.Errorf("uptime_human = %q, want a duration under a minute (%v)",
 			human, err)
 	}
 
-	seconds, ok := body["uptimeSeconds"].(float64)
+	seconds, ok := body["uptime_seconds"].(float64)
 	if !ok || seconds < 0 || seconds > time.Minute.Seconds() {
-		t.Errorf("uptimeSeconds = %v, want a number of seconds under a minute",
-			body["uptimeSeconds"])
+		t.Errorf("uptime_seconds = %v, want a number of seconds under a minute",
+			body["uptime_seconds"])
 	}
 }

backend/internal/healthcheck/healthcheck.go

@@ -30,14 +30,17 @@ type Healthcheck struct {
 	params      *Params
 }
 
-// Response is the JSON payload returned by the health check
-// endpoint.
-type Response struct {
+// HealthcheckResponse is the JSON payload returned by the health
+// check endpoint. Its name and its snake_case keys are the ones
+// GO_HTTP_SERVER_CONVENTIONS.md gives.
+//
+//nolint:revive,tagliatelle // name and keys from the conventions
+type HealthcheckResponse struct {
 	Appname       string `json:"appname"`
 	Now           string `json:"now"`
 	Status        string `json:"status"`
-	UptimeHuman   string `json:"uptimeHuman"`
-	UptimeSeconds int64  `json:"uptimeSeconds"`
+	UptimeHuman   string `json:"uptime_human"`
+	UptimeSeconds int64  `json:"uptime_seconds"`
 	Version       string `json:"version"`
 }
 
@@ -65,9 +68,9 @@ func New(
 	return s, nil
 }
 
-// Check returns the current health status of the application.
-func (s *Healthcheck) Check() *Response {
-	return &Response{
+// Healthcheck returns the current health status of the application.
+func (s *Healthcheck) Healthcheck() *HealthcheckResponse {
+	return &HealthcheckResponse{
 		Appname:       s.params.Globals.Appname,
 		Now:           time.Now().UTC().Format(time.RFC3339Nano),
 		Status:        "ok",

package.json

@@ -6,7 +6,8 @@
     "scripts": {
         "dev": "vite",
         "build": "vite build",
-        "preview": "vite preview"
+        "preview": "vite preview",
+        "test": "node --test test/unit/*.test.js"
     },
     "license": "MIT",
     "devDependencies": {

script/frontend-test

@@ -1,14 +1,22 @@
 #!/bin/sh
 # script/frontend-test: run the frontend test suite: the unit tests in
-# test/unit/ with Node's built-in test runner, then the production
-# build, which fails on broken code.
+# test/unit/, through the test script in package.json, then the
+# production build, which fails on broken code. The tests print a dot
+# each; if any fails, they run again with every test listed, and the
+# script fails even if that run passes. NODE_OPTIONS chooses the
+# reporter because yarn adds its arguments after the test files, where
+# node would take a reporter option for one more file.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    timeout 30 node --test test/unit/*.test.js
+    NODE_OPTIONS=--test-reporter=dot timeout 30 yarn --silent run test || {
+        echo "--- Rerunning with every test listed for details ---"
+        NODE_OPTIONS=--test-reporter=spec timeout 30 yarn --silent run test
+        exit 1
+    }
     timeout 30 yarn build
 }
 

src/main.js

@@ -151,7 +151,7 @@ function formatUTCTimestamp(date) {
 
 // --- Duration Formatting -----------------------------------------------------
 
-function humanDuration(seconds) {
+export function humanDuration(seconds) {
     const h = Math.floor(seconds / 3600);
     const m = Math.floor((seconds % 3600) / 60);
     const s = seconds % 60;
@@ -197,7 +197,7 @@ async function detectGateway() {
 
 // --- App State ---------------------------------------------------------------
 
-class HostState {
+export class HostState {
     constructor(host, pinned = false) {
         this.name = host.name;
         this.url = host.url;
@@ -546,7 +546,7 @@ export async function measureLatency(url, signal) {
 
 // --- Color Helpers -----------------------------------------------------------
 
-function latencyHex(latency) {
+export function latencyHex(latency) {
     if (latency === null) return "#6b7280";
     if (latency < 50) return "#22c55e";
     if (latency < 100) return "#84cc16";
@@ -555,7 +555,7 @@ function latencyHex(latency) {
     return "#ef4444";
 }
 
-function latencyClass(latency, status) {
+export function latencyClass(latency, status) {
     if (status === "offline" || status === "error" || latency === null)
         return "text-gray-500";
     if (latency < 50) return "text-green-500";

test/unit/main.test.js

@@ -1,5 +1,6 @@
-// Unit tests for src/main.js, run by script/frontend-test with Node's
-// built-in test runner. Importing the module does not start the page.
+// Unit tests for src/main.js, run with Node's built-in test runner by the
+// test script in package.json. Importing the module does not start the
+// page.
 
 import { beforeEach, test } from "node:test";
 import assert from "node:assert/strict";
@@ -7,6 +8,10 @@ import {
     AppState,
     CONFIG,
     greyOutUI,
+    HostState,
+    humanDuration,
+    latencyClass,
+    latencyHex,
     measureLatency,
     tick,
 } from "../../src/main.js";
@@ -224,3 +229,161 @@ test("at a 30000ms interval, after the user pauses and resumes during a round, n
         assert.notEqual(statusText(state, host), "paused", host.name);
     }
 });
+
+for (const [seconds, text] of [
+    [0, "0s"],
+    [1, "1s"],
+    [59, "59s"],
+    [60, "1m"],
+    [61, "1m1s"],
+    [3599, "59m59s"],
+    [3600, "1h"],
+    [3601, "1h1s"],
+    [3660, "1h1m"],
+    [3661, "1h1m1s"],
+]) {
+    test(`humanDuration writes ${seconds} seconds as ${text}`, () => {
+        assert.equal(humanDuration(seconds), text);
+    });
+}
+
+// The colour of a target's latency figure, as a class, and of its sparkline
+// for an answer after latency ms, as the colour coding in README.md gives
+// them. The rows sit either side of each boundary.
+for (const [latency, figure, sparkline] of [
+    [0, "text-green-500", "#22c55e"],
+    [49, "text-green-500", "#22c55e"],
+    [50, "text-lime-500", "#84cc16"],
+    [99, "text-lime-500", "#84cc16"],
+    [100, "text-yellow-500", "#eab308"],
+    [199, "text-yellow-500", "#eab308"],
+    [200, "text-orange-500", "#f97316"],
+    [499, "text-orange-500", "#f97316"],
+    [500, "text-red-500", "#ef4444"],
+]) {
+    test(`an answer after ${latency}ms has a ${figure} figure and a ${sparkline} sparkline`, () => {
+        assert.equal(latencyClass(latency, "online"), figure);
+        assert.equal(latencyHex(latency), sparkline);
+    });
+}
+
+test("a check that timed out or found its target unreachable has a grey figure and sparkline", () => {
+    assert.equal(latencyClass(null, "error"), "text-gray-500");
+    assert.equal(latencyClass(null, "offline"), "text-gray-500");
+    assert.equal(latencyHex(null), "#6b7280");
+});
+
+// A target whose checks, in turn, answered after each of latencies ms, or,
+// for null, found it unreachable.
+function hostAfter(latencies) {
+    const host = new HostState({ name: "Target", url: "https://target.test" });
+    for (const latency of latencies) {
+        host.pushSample(
+            Date.now(),
+            latency === null
+                ? { latency: null, error: "unreachable" }
+                : { latency, error: null },
+        );
+    }
+    return host;
+}
+
+for (const { history, latencies, statistics } of [
+    {
+        history: "no checks",
+        latencies: [],
+        statistics: { min: null, max: null, average: null, median: null },
+    },
+    {
+        history: "only unreachable checks",
+        latencies: [null, null, null],
+        statistics: { min: null, max: null, average: null, median: null },
+    },
+    {
+        history: "three answers and an unreachable check",
+        latencies: [30, null, 10, 20],
+        statistics: { min: 10, max: 30, average: 20, median: 20 },
+    },
+    {
+        // The median of an even number of answers is the mean of the
+        // middle two. It and the average, 23.75, are rounded.
+        history: "four answers",
+        latencies: [10, 40, 20, 25],
+        statistics: { min: 10, max: 40, average: 24, median: 23 },
+    },
+    {
+        // Sorted as text rather than as numbers, these answers would put
+        // 100 in the middle. The average, 39.67, is rounded.
+        history: "answers with different numbers of digits",
+        latencies: [100, 9, 10],
+        statistics: { min: 9, max: 100, average: 40, median: 10 },
+    },
+]) {
+    test(`a target's min, max, average and median latency over ${history}`, () => {
+        const host = hostAfter(latencies);
+        assert.deepEqual(
+            {
+                min: host.minLatency(),
+                max: host.maxLatency(),
+                average: host.averageLatency(),
+                median: host.medianLatency(),
+            },
+            statistics,
+        );
+    });
+}
+
+// An app state in which, of the WAN targets, the first timedOut timed out,
+// the next unreachable were found unreachable, the next answered answered
+// after latency ms, and the rest have not been checked yet.
+function stateAfter({ timedOut, unreachable, answered, latency }) {
+    const state = new AppState([]);
+    const results = [
+        ...Array(timedOut).fill({ latency: null, error: "timeout" }),
+        ...Array(unreachable).fill({ latency: null, error: "unreachable" }),
+        ...Array(answered).fill({ latency, error: null }),
+    ];
+    results.forEach((result, i) => state.wan[i].pushSample(Date.now(), result));
+    return state;
+}
+
+// For each number the health is decided by, the rows put it one under, at
+// and one over its threshold.
+for (const { timedOut, unreachable = 0, answered, latency, health } of [
+    // Offline: more than 10 timed out and at most 4 answered.
+    { timedOut: 9, answered: 4, latency: 30, health: "degraded" },
+    { timedOut: 10, answered: 4, latency: 30, health: "degraded" },
+    { timedOut: 11, answered: 4, latency: 30, health: "offline" },
+    { timedOut: 11, answered: 3, latency: 30, health: "offline" },
+    { timedOut: 11, answered: 5, latency: 30, health: "degraded" },
+    // Otherwise degraded: more than 4 timed out.
+    { timedOut: 3, answered: 10, latency: 30, health: "healthy" },
+    { timedOut: 4, answered: 10, latency: 30, health: "healthy" },
+    { timedOut: 5, answered: 10, latency: 30, health: "degraded" },
+    // Otherwise slow: more than 3 answered after more than 1000ms.
+    { timedOut: 0, answered: 4, latency: 999, health: "healthy" },
+    { timedOut: 0, answered: 4, latency: 1000, health: "healthy" },
+    { timedOut: 0, answered: 4, latency: 1001, health: "slow" },
+    { timedOut: 0, answered: 2, latency: 1001, health: "healthy" },
+    { timedOut: 0, answered: 3, latency: 1001, health: "healthy" },
+    // A target found unreachable counts as one that timed out.
+    {
+        timedOut: 5,
+        unreachable: 6,
+        answered: 4,
+        latency: 30,
+        health: "offline",
+    },
+    {
+        timedOut: 0,
+        unreachable: 5,
+        answered: 10,
+        latency: 30,
+        health: "degraded",
+    },
+]) {
+    test(`with ${timedOut} WAN targets timed out, ${unreachable} found unreachable and ${answered} answering after ${latency}ms, the health is ${health}`, () => {
+        const state = stateAfter({ timedOut, unreachable, answered, latency });
+        assert.equal(state.healthStatus(), health);
+    });
+}