Refine VPN client instructions and subscription refresh flow

test/server/subscription.test.js

@@ -1,7 +1,10 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
 
-import { parseSubscriptionBody } from '../../src/server/subscription.js';
+import {
+  parseSubscriptionBody,
+  selectRefreshedServer,
+} from '../../src/server/subscription.js';
 
 test('subscription server tags are trimmed for selection', () => {
   const { servers } = parseSubscriptionBody(JSON.stringify({
@@ -10,3 +13,19 @@ test('subscription server tags are trimmed for selection', () => {
 
   assert.equal(servers[0].tag, 'de-frankfurt');
 });
+
+test('refreshed subscription keeps the selected server when its tag still exists', () => {
+  const servers = [{ tag: 'de' }, { tag: 'nl' }];
+
+  assert.equal(selectRefreshedServer('nl', servers), 'nl');
+});
+
+test('refreshed subscription selects the first server when the old tag disappeared', () => {
+  const servers = [{ tag: 'de' }, { tag: 'nl' }];
+
+  assert.equal(selectRefreshedServer('old-name', servers), 'de');
+});
+
+test('refreshed subscription does not select a server before the first user choice', () => {
+  assert.equal(selectRefreshedServer('', [{ tag: 'de' }]), '');
+});