Refactor server picker and limit ping requests

test/server/server-health.test.js

@@ -0,0 +1,26 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { checkServerHealth } from '../../src/server/serverHealth.js';
+
+test('server health checks cap count and concurrency', async () => {
+  const servers = Array.from({ length: 300 }, (_, index) => ({
+    id: `srv-${index}`,
+    label: `Server ${index}`,
+    host: `server-${index}.example`,
+    port: 443,
+  }));
+  let active = 0;
+  let peak = 0;
+  const results = await checkServerHealth(servers, async () => {
+    active += 1;
+    peak = Math.max(peak, active);
+    await new Promise((resolve) => setImmediate(resolve));
+    active -= 1;
+    return { ok: true, latency: 1 };
+  });
+
+  assert.equal(results.length, 30);
+  assert.equal(peak, 4);
+  assert.deepEqual(results.map(({ id }) => id), servers.slice(0, 30).map(({ id }) => id));
+});