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 empty, all-unreachable and
mixed histories, and the four health states either side of their
thresholds. 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

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 +229,140 @@ 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 },
+    },
+]) {
+    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 answered answered after latency ms, and the rest have not been
+// checked yet.
+function stateAfter({ timedOut, answered, latency }) {
+    const state = new AppState([]);
+    for (const host of state.wan.slice(0, timedOut)) {
+        host.pushSample(Date.now(), { latency: null, error: "timeout" });
+    }
+    for (const host of state.wan.slice(timedOut, timedOut + answered)) {
+        host.pushSample(Date.now(), { latency, error: null });
+    }
+    return state;
+}
+
+// For each number the health is decided by, the rows put it one under, at
+// and one over its threshold. A target found unreachable counts as one
+// that timed out.
+for (const { timedOut, 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" },
+]) {
+    test(`with ${timedOut} WAN targets timed out and ${answered} answering after ${latency}ms, the health is ${health}`, () => {
+        const state = stateAfter({ timedOut, answered, latency });
+        assert.equal(state.healthStatus(), health);
+    });
+}