What happens in tests when the requested port is in use? What's verified?

When a requested port is in use, the tests verify two key behaviors:

1. Single preferred port unavailable: In [test.js:L24-L32], when a specific preferred port (8282) is already bound by a server, the test verifies that:

• getPort() still returns a valid port number
• The returned port is greater than 0
• The returned port is not the desired unavailable port (8282)

test('preferred port unavailable', async t => {
	const desiredPort = 8282;
	const server = net.createServer();
	await promisify(server.listen.bind(server))(desiredPort);

	const port = await getPort({port: desiredPort});
	t.is(typeof port, 'number');
	t.true(port > 0);
	t.not(port, desiredPort);
});

2. All preferred ports unavailable: In [test.js:L91-L108], when multiple preferred ports are in use, the test confirms that:

• A different port is selected instead
• The returned port is valid (between 0 and 65,536)
• It matches neither of the unavailable preferred ports

This demonstrates that getPort() falls back to finding an available port when preferred options aren't accessible, rather than failing.

FOLLOW_UPS:

• How does getPort handle array vs single preferred ports?
• What's the purpose of the reserve option in tests?
• How does the exclude option affect port selection?