test: search the full random port range

tests/e2e/get-random-port.test.js

@@ -0,0 +1,37 @@
+const {
+  getRandomPorts,
+  releaseRandomPorts,
+} = require('../helpers/get-random-port');
+
+describe('random port allocation', () => {
+  let ports = [];
+
+  afterEach(() => {
+    releaseRandomPorts(ports);
+    ports = [];
+    rstest.restoreAllMocks();
+  });
+
+  it('allocates a contiguous block when the random start is at the upper boundary', async () => {
+    rstest.spyOn(Math, 'random').mockReturnValue(0.99999);
+    ports = await getRandomPorts(8, '127.0.0.1');
+
+    expect(ports).toHaveLength(8);
+    expect(ports[0]).toBeGreaterThanOrEqual(15000);
+    expect(ports[7]).toBeLessThanOrEqual(45000);
+    expect(ports).toEqual(Array.from({ length: 8 }, (_, i) => ports[0] + i));
+  });
+
+  it('wraps to lower ports when the upper block is already reserved', async () => {
+    rstest.spyOn(Math, 'random').mockReturnValue(0.99999);
+    const first = await getRandomPorts(8, '127.0.0.1');
+    ports.push(...first);
+    const second = await getRandomPorts(8, '127.0.0.1');
+    ports.push(...second);
+
+    expect(new Set(ports).size).toBe(16);
+    expect(second).toEqual(Array.from({ length: 8 }, (_, i) => second[0] + i));
+    expect(second[0]).toBeGreaterThanOrEqual(15000);
+    expect(second[7]).toBeLessThanOrEqual(45000);
+  });
+});

tests/helpers/get-random-port.js

@@ -32,10 +32,15 @@ function getDefaultPort() {
 }
 
 async function findAvailablePort(startPort, count, host) {
-  let port = Math.max(startPort, minRandomPort);
   const maxStartPort = maxRandomPort - count + 1;
-
-  while (port <= maxStartPort) {
+  let port = Math.min(Math.max(startPort, minRandomPort), maxStartPort);
+
+  // Search every valid start once, including ports below the random start.
+  for (
+    let remaining = maxStartPort - minRandomPort + 1;
+    remaining > 0;
+    remaining -= 1
+  ) {
     let isAvailable = true;
 
     for (let index = 0; index < count; index += 1) {
@@ -54,7 +59,7 @@ async function findAvailablePort(startPort, count, host) {
       return port;
     }
 
-    port += 1;
+    port = port === maxStartPort ? minRandomPort : port + 1;
   }
 
   throw new Error('No available ports found');