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

Question

RepoPilot · Accepted Answer

When the requested port is in use, the tests verify that `get-port` falls back to finding an alternative available port instead of returning the unavailable one.

For example, in the test "first port in preferred ports array is unavailable" [test.js:L81-L95], a server is bound to the first desired port (9090), and then `getPort()` is called with that port in the preferred ports array. The test verifies that the function returns the second port (9091) instead:

```javascript
const desiredPorts = [9090, 9091];
const server = net.createServer();
await promisify(server.listen.bind(server))(desiredPorts[0]);

const port = await getPort({
	port: desiredPorts,
});

t.is(port, desiredPorts[1]);
```

Similarly, the test "all preferred ports in array are unavailable" [test.js:L97-L120] verifies that when **all** preferred ports are occupied, `getPort()` returns a random available port that is neither of the preferred ones:

```javascript
t.is(typeof port, 'number');
t.true(port > 0 && port < 65_536);
t.not(port, desiredPorts[0]);
t.not(port, desiredPorts[1]);
```

There's also a test for a single unavailable preferred port [test.js:L35-L41] that verifies a different port is returned when the desired one is taken.

FOLLOW_UPS:
- How does the locking mechanism prevent race conditions?
- What's the difference between reserve true and false?
- Can you exclude specific ports from being returned?