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 and one of only answers, 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

test/unit/main.test.js

@@ -327,23 +327,22 @@ for (const { history, latencies, statistics } of [
 }
 
 // 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 }) {
+// 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([]);
-    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 });
-    }
+    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. A target found unreachable counts as one
-// that timed out.
-for (const { timedOut, answered, latency, health } of [
+// 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" },
@@ -360,9 +359,24 @@ for (const { timedOut, answered, latency, health } of [
     { 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 and ${answered} answering after ${latency}ms, the health is ${health}`, () => {
-        const state = stateAfter({ timedOut, answered, latency });
+    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);
     });
 }