test: unit test the port finding function

test/server/get-port.test.js

@@ -0,0 +1,36 @@
+"use strict";
+
+const net = require("net");
+const util = require("util");
+const getPort = require("../../lib/getPort");
+
+it("it should bind to the preferred port", async () => {
+  const preferredPort = 8080;
+  const port = await getPort(8080);
+  expect(port).toBe(preferredPort);
+});
+
+it("should pick the next port if the preferred port is unavailable", async () => {
+  const preferredPort = 8345;
+  const server = net.createServer();
+  server.unref();
+  await util.promisify(server.listen.bind(server))(preferredPort);
+  const port = await getPort(preferredPort);
+  expect(port).toBe(preferredPort + 1);
+});
+
+it("should reject privileged ports", async () => {
+  try {
+    await getPort(80);
+  } catch (e) {
+    expect(e.message).toBeDefined();
+  }
+});
+
+it("should reject too high port numbers", async () => {
+  try {
+    await getPort(65536);
+  } catch (e) {
+    expect(e.message).toBeDefined();
+  }
+});