Validate fake synchronization checkpoints

Author: stevebauman

src/Testing/FakeMessageQuery.php

@@ -20,6 +20,7 @@
 use DirectoryTree\ImapEngine\UidOrder;
 use DirectoryTree\ImapEngine\Vanished;
 use Illuminate\Support\ItemNotFoundException;
+use InvalidArgumentException;
 
 class FakeMessageQuery implements MessageQueryInterface
 {
@@ -56,6 +57,10 @@ public function changesSince(int $modSequence, array|int $uids, bool $vanished =
             return new FetchResult;
         }
 
+        if ($modSequence < 0) {
+            throw new InvalidArgumentException('Invalid IMAP modification sequence.');
+        }
+
         $capability = $vanished ? 'QRESYNC' : 'CONDSTORE';
 
         $mailbox = $this->folder->mailbox();

tests/Unit/Testing/FakeMessageQueryTest.php

@@ -347,6 +347,13 @@
     expect($result->vanishedUids())->toBe([]);
 });
 
+test('fake synchronization rejects negative checkpoints for a non-empty uid set', function () {
+    $folder = new FakeFolder('INBOX', messages: [new FakeMessage(7)]);
+
+    expect(fn () => $folder->messages()->changesSince(-1, [7]))
+        ->toThrow(InvalidArgumentException::class);
+});
+
 test('fake synchronization returns messages that vanished after the checkpoint', function () {
     $folder = new FakeFolder(
         'INBOX',