diff --git a/tests/Sync/FoldersTest.php b/tests/Sync/FoldersTest.php
index ed234c5..91cf0f0 100644
--- a/tests/Sync/FoldersTest.php
+++ b/tests/Sync/FoldersTest.php
@@ -1,389 +1,467 @@
 <?php
 
 class FoldersTest extends Tests\SyncTestCase
 {
     /**
-     * Test FolderSync command
+     * Cleanup folders
      */
-    public function testFolderSync()
+    public function setUp(): void
     {
         // Note: We essentially assume the test account is in an initial state, extra folders may break tests
         // Anyway, we first remove folders that might have been created during tests in this file
         $this->deleteTestFolder('Test Folder', 'mail');
         $this->deleteTestFolder('Test Folder New', 'mail');
         $this->deleteTestFolder('Test Contacts Folder', 'contact');
         $this->deleteTestFolder('Test Contacts New', 'contact');
+        parent::setUp();
+    }
+
+    /**
+     * Test FolderSync command
+     */
+    public function testFolderSyncBasic()
+    {
+        $request = <<<EOF
+            <?xml version="1.0" encoding="utf-8"?>
+            <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
+            <FolderSync xmlns="uri:FolderHierarchy">
+                <SyncKey>0</SyncKey>
+            </FolderSync>
+            EOF;
+
+        $response = $this->request($request, 'FolderSync');
+
+        $this->assertEquals(200, $response->getStatusCode());
+
+        $dom = $this->fromWbxml($response->getBody());
+        $xpath = $this->xpath($dom);
+
+        $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:Status")->item(0)->nodeValue);
+        $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:SyncKey")->item(0)->nodeValue);
+        // We expect some folders to exist (dont' know how many)
+        $this->assertTrue(intval($xpath->query("//ns:FolderSync/ns:Changes/ns:Count")->item(0)->nodeValue) > 2);
+
+        $request = <<<EOF
+            <?xml version="1.0" encoding="utf-8"?>
+            <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
+            <FolderSync xmlns="uri:FolderHierarchy">
+                <SyncKey>1</SyncKey>
+            </FolderSync>
+            EOF;
+
+        $response = $this->request($request, 'FolderSync');
+
+        $this->assertEquals(200, $response->getStatusCode());
+
+        $dom = $this->fromWbxml($response->getBody());
+        $xpath = $this->xpath($dom);
+
+        $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:Status")->item(0)->nodeValue);
+        $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:SyncKey")->item(0)->nodeValue);
+        // No changes on second sync
+        $this->assertSame(strval(0), $xpath->query("//ns:FolderSync/ns:Changes/ns:Count")->item(0)->nodeValue);
+    }
+
+    /**
+     * Test invalid sync key
+     */
+    public function testFolderInvalidSyncKey()
+    {
+        $request = <<<EOF
+            <?xml version="1.0" encoding="utf-8"?>
+            <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
+            <FolderSync xmlns="uri:FolderHierarchy">
+                <SyncKey>999</SyncKey>
+            </FolderSync>
+            EOF;
+
+        $response = $this->request($request, 'FolderSync');
+
+        $this->assertEquals(200, $response->getStatusCode());
+
+        $dom = $this->fromWbxml($response->getBody());
+        $xpath = $this->xpath($dom);
+
+        $this->assertSame('9', $xpath->query("//ns:FolderSync/ns:Status")->item(0)->nodeValue);
+    }
+
+
+    /**
+     * Test FolderSync command
+     */
+    public function testFolderSync()
+    {
 
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderSync xmlns="uri:FolderHierarchy">
                 <SyncKey>0</SyncKey>
             </FolderSync>
             EOF;
 
         $response = $this->request($request, 'FolderSync');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         // Note: We're expecting activesync_init_subscriptions=0 here.
         if ($this->isStorageDriver('kolab4')) {
             $folders = [
                 ['Calendar', Syncroton_Command_FolderSync::FOLDERTYPE_CALENDAR],
                 ['Contacts', Syncroton_Command_FolderSync::FOLDERTYPE_CONTACT],
                 ['INBOX', Syncroton_Command_FolderSync::FOLDERTYPE_INBOX],
                 ['Drafts', Syncroton_Command_FolderSync::FOLDERTYPE_DRAFTS],
                 ['Sent', Syncroton_Command_FolderSync::FOLDERTYPE_SENTMAIL],
                 ['Trash', Syncroton_Command_FolderSync::FOLDERTYPE_DELETEDITEMS],
                 ['Tasks', Syncroton_Command_FolderSync::FOLDERTYPE_TASK],
             ];
 
         } else {
             $folders = [
                 ['Calendar', Syncroton_Command_FolderSync::FOLDERTYPE_CALENDAR],
                 ['Contacts', Syncroton_Command_FolderSync::FOLDERTYPE_CONTACT],
                 ['INBOX', Syncroton_Command_FolderSync::FOLDERTYPE_INBOX],
                 ['Drafts', Syncroton_Command_FolderSync::FOLDERTYPE_DRAFTS],
                 ['Sent', Syncroton_Command_FolderSync::FOLDERTYPE_SENTMAIL],
                 ['Trash', Syncroton_Command_FolderSync::FOLDERTYPE_DELETEDITEMS],
                 ['Notes', Syncroton_Command_FolderSync::FOLDERTYPE_NOTE],
                 ['Tasks', Syncroton_Command_FolderSync::FOLDERTYPE_TASK],
             ];
         }
 
         $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:Status")->item(0)->nodeValue);
         $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:SyncKey")->item(0)->nodeValue);
         $this->assertSame(strval(count($folders)), $xpath->query("//ns:FolderSync/ns:Changes/ns:Count")->item(0)->nodeValue);
 
         foreach ($folders as $idx => $folder) {
             $this->assertSame($folder[0], $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:DisplayName")->item($idx)->nodeValue);
             $this->assertSame((string) $folder[1], $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:Type")->item($idx)->nodeValue);
             $this->assertSame('0', $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:ParentId")->item($idx)->nodeValue);
         }
 
         // Test with multi-folder support enabled
         self::$deviceType = 'iphone';
 
         $response = $this->request($request, 'FolderSync');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         if ($this->isStorageDriver('kolab4')) {
             $folders = [
                 ['Calendar', Syncroton_Command_FolderSync::FOLDERTYPE_CALENDAR],
                 // Note: Kolab 4 with Cyrus DAV uses Addressbook, but Kolab 3 with iRony would use 'Contacts'
                 ['/^(Contacts|Addressbook)$/', Syncroton_Command_FolderSync::FOLDERTYPE_CONTACT],
                 ['INBOX', Syncroton_Command_FolderSync::FOLDERTYPE_INBOX],
                 ['Drafts', Syncroton_Command_FolderSync::FOLDERTYPE_DRAFTS],
                 ['Sent', Syncroton_Command_FolderSync::FOLDERTYPE_SENTMAIL],
                 ['Trash', Syncroton_Command_FolderSync::FOLDERTYPE_DELETEDITEMS],
                 // Note: For now Kolab 4 uses the same Calendar folder for calendar and tasks
                 ['/^(Tasks|Calendar)$/', Syncroton_Command_FolderSync::FOLDERTYPE_TASK],
             ];
         }
 
         $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:Status")->item(0)->nodeValue);
         $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:SyncKey")->item(0)->nodeValue);
         $this->assertSame(strval(count($folders)), $xpath->query("//ns:FolderSync/ns:Changes/ns:Count")->item(0)->nodeValue);
 
         foreach ($folders as $idx => $folder) {
             $displayName = $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:DisplayName")->item($idx)->nodeValue;
             if (str_starts_with($folder[0], '/')) {
                 $this->assertMatchesRegularExpression($folder[0], $displayName);
             } else {
                 $this->assertSame($folder[0], $displayName);
             }
             $this->assertSame((string) $folder[1], $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:Type")->item($idx)->nodeValue);
             $this->assertSame('0', $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:ParentId")->item($idx)->nodeValue);
             $idx++;
         }
 
         // After we switched to multi-folder supported mode we expect next FolderSync
         // to delete the old "collective" folders
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderSync xmlns="uri:FolderHierarchy">
                 <SyncKey>1</SyncKey>
             </FolderSync>
             EOF;
 
         $response = $this->request($request, 'FolderSync');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         $deleted = $this->isStorageDriver('kolab4') ? 3 : 4; // No Notes folder in Kolab4
         $syncKey = 2;
 
         $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval($syncKey), $xpath->query("//ns:FolderSync/ns:SyncKey")->item(0)->nodeValue);
         $this->assertSame(strval($deleted), $xpath->query("//ns:FolderSync/ns:Changes/ns:Count")->item(0)->nodeValue);
         $this->assertSame($deleted, $xpath->query("//ns:FolderSync/ns:Changes/ns:Delete")->length);
 
         return $syncKey;
     }
 
     /**
      * Test FolderCreate command
      *
      * @depends testFolderSync
      */
     public function testFolderCreate($syncKey)
     {
         // Multi-folder mode
         self::$deviceType = 'iphone';
 
         // Create a mail folder
         $folderName1 = 'Test Folder';
         $folderType = Syncroton_Command_FolderSync::FOLDERTYPE_MAIL_USER_CREATED;
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderCreate xmlns="uri:FolderHierarchy">
                 <SyncKey>{$syncKey}</SyncKey>
                 <ParentId>0</ParentId>
                 <DisplayName>{$folderName1}</DisplayName>
                 <Type>{$folderType}</Type>
             </FolderCreate>
             EOF;
 
         $response = $this->request($request, 'FolderCreate');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         $this->assertSame('1', $xpath->query("//ns:FolderCreate/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval(++$syncKey), $xpath->query("//ns:FolderCreate/ns:SyncKey")->item(0)->nodeValue);
         $this->assertSame(1, $xpath->query("//ns:FolderCreate/ns:ServerId")->count());
         $folder1 = $xpath->query("//ns:FolderCreate/ns:ServerId")->item(0)->nodeValue;
 
         // Note: After FolderCreate there are no changes in the following FolderSync expected
 
         // Create a contacts folder
         $folderName2 = 'Test Contacts Folder';
         $folderType = Syncroton_Command_FolderSync::FOLDERTYPE_CONTACT_USER_CREATED;
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderCreate xmlns="uri:FolderHierarchy">
                 <SyncKey>{$syncKey}</SyncKey>
                 <ParentId>0</ParentId>
                 <DisplayName>{$folderName2}</DisplayName>
                 <Type>{$folderType}</Type>
             </FolderCreate>
             EOF;
 
         $response = $this->request($request, 'FolderCreate');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         $this->assertSame('1', $xpath->query("//ns:FolderCreate/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval(++$syncKey), $xpath->query("//ns:FolderCreate/ns:SyncKey")->item(0)->nodeValue);
         $this->assertSame(1, $xpath->query("//ns:FolderCreate/ns:ServerId")->count());
         $folder2 = $xpath->query("//ns:FolderCreate/ns:ServerId")->item(0)->nodeValue;
 
         // Note: After FolderCreate there are no changes in the following FolderSync expected
 
         // TODO: Test folder with a parent
 
         return [
             'SyncKey' => $syncKey,
             'folders' => [
                 $folder1,
                 $folder2,
             ],
         ];
     }
 
     /**
      * Test FolderUpdate command
      *
      * @depends testFolderCreate
      */
     public function testFolderUpdate($params)
     {
         // Multi-folder mode
         self::$deviceType = 'iphone';
 
         // Test renaming a mail folder
         $folderType = Syncroton_Command_FolderSync::FOLDERTYPE_MAIL_USER_CREATED;
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderUpdate xmlns="uri:FolderHierarchy">
                 <SyncKey>{$params['SyncKey']}</SyncKey>
                 <ServerId>{$params['folders'][0]}</ServerId>
                 <ParentId/>
                 <DisplayName>Test Folder New</DisplayName>
                 <Type>{$folderType}</Type>
             </FolderUpdate>
             EOF;
 
         $response = $this->request($request, 'FolderUpdate');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         $this->assertSame('1', $xpath->query("//ns:FolderUpdate/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval(++$params['SyncKey']), $xpath->query("//ns:FolderUpdate/ns:SyncKey")->item(0)->nodeValue);
 
         // Test FolderSync after folder update, get the new folder id (for delete test)
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderSync xmlns="uri:FolderHierarchy">
                 <SyncKey>{$params['SyncKey']}</SyncKey>
             </FolderSync>
             EOF;
 
         $response = $this->request($request, 'FolderSync');
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         // Note we expect Add+Delete here, instead of Update (but this could change in the future)
         $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval(++$params['SyncKey']), $xpath->query("//ns:FolderSync/ns:SyncKey")->item(0)->nodeValue);
         $this->assertSame(1, $xpath->query("//ns:FolderSync/ns:Changes/ns:Add")->length);
         $this->assertSame(1, $xpath->query("//ns:FolderSync/ns:Changes/ns:Delete")->length);
         $this->assertSame($params['folders'][0], $xpath->query("//ns:FolderSync/ns:Changes/ns:Delete/ns:ServerId")->item(0)->nodeValue);
         $this->assertSame('0', $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:ParentId")->item(0)->nodeValue);
         $this->assertSame('Test Folder New', $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:DisplayName")->item(0)->nodeValue);
         $this->assertSame(strval($folderType), $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:Type")->item(0)->nodeValue);
         $params['folders'][0] = $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:ServerId")->item(0)->nodeValue;
 
         // Test renaming a contacts folder
         $folderType = Syncroton_Command_FolderSync::FOLDERTYPE_CONTACT_USER_CREATED;
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderUpdate xmlns="uri:FolderHierarchy">
                 <SyncKey>{$params['SyncKey']}</SyncKey>
                 <ServerId>{$params['folders'][1]}</ServerId>
                 <ParentId/>
                 <DisplayName>Test Contacts New</DisplayName>
                 <Type>{$folderType}</Type>
             </FolderUpdate>
             EOF;
 
         $response = $this->request($request, 'FolderUpdate');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         $this->assertSame('1', $xpath->query("//ns:FolderUpdate/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval(++$params['SyncKey']), $xpath->query("//ns:FolderUpdate/ns:SyncKey")->item(0)->nodeValue);
 
         // Test FolderSync after folder update, get the new folder id (for delete test)
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderSync xmlns="uri:FolderHierarchy">
                 <SyncKey>{$params['SyncKey']}</SyncKey>
             </FolderSync>
             EOF;
 
         $response = $this->request($request, 'FolderSync');
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval(++$params['SyncKey']), $xpath->query("//ns:FolderSync/ns:SyncKey")->item(0)->nodeValue);
 
         if ($this->isStorageDriver('kolab4')) {
             // Note we expect Update here, not Add+Delete, folder ID does not change
             $this->assertSame('1', $xpath->query("//ns:FolderSync/ns:Changes/ns:Count")->item(0)->nodeValue);
             $this->assertSame($params['folders'][1], $xpath->query("//ns:FolderSync/ns:Changes/ns:Update/ns:ServerId")->item(0)->nodeValue);
             $this->assertSame('Test Contacts New', $xpath->query("//ns:FolderSync/ns:Changes/ns:Update/ns:DisplayName")->item(0)->nodeValue);
             $this->assertSame(strval($folderType), $xpath->query("//ns:FolderSync/ns:Changes/ns:Update/ns:Type")->item(0)->nodeValue);
         } else {
             // Note we expect Add+Delete here, instead of Update (but this could change in the future)
             $this->assertSame('2', $xpath->query("//ns:FolderSync/ns:Changes/ns:Count")->item(0)->nodeValue);
             $this->assertSame($params['folders'][1], $xpath->query("//ns:FolderSync/ns:Changes/ns:Delete/ns:ServerId")->item(0)->nodeValue);
             $this->assertSame('0', $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:ParentId")->item(0)->nodeValue);
             $this->assertSame('Test Contacts New', $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:DisplayName")->item(0)->nodeValue);
             $this->assertSame(strval($folderType), $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:Type")->item(0)->nodeValue);
             $params['folders'][1] = $xpath->query("//ns:FolderSync/ns:Changes/ns:Add/ns:ServerId")->item(0)->nodeValue;
         }
 
         // TODO: Test folder with a parent change
         // TODO: Assert the folder name has changed in the storage
         // TODO: Test Sync after a DAV folder rename made in another client
 
         return $params;
     }
 
     /**
      * Test FolderDelete command
      *
      * @depends testFolderUpdate
      */
     public function testFolderDelete($params)
     {
         // Multi-folder mode
         self::$deviceType = 'iphone';
 
         // Delete mail folder
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderDelete xmlns="uri:FolderHierarchy">
                 <SyncKey>{$params['SyncKey']}</SyncKey>
                 <ServerId>{$params['folders'][0]}</ServerId>
             </FolderDelete>
             EOF;
 
         $response = $this->request($request, 'FolderDelete');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         $this->assertSame('1', $xpath->query("//ns:FolderDelete/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval(++$params['SyncKey']), $xpath->query("//ns:FolderDelete/ns:SyncKey")->item(0)->nodeValue);
 
         // Note: After FolderDelete there are no changes in the following FolderSync expected
 
         // Delete contacts folder
         $request = <<<EOF
             <?xml version="1.0" encoding="utf-8"?>
             <!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" "http://www.microsoft.com/">
             <FolderDelete xmlns="uri:FolderHierarchy">
                 <SyncKey>{$params['SyncKey']}</SyncKey>
                 <ServerId>{$params['folders'][1]}</ServerId>
             </FolderDelete>
             EOF;
 
         $response = $this->request($request, 'FolderDelete');
 
         $this->assertEquals(200, $response->getStatusCode());
 
         $dom = $this->fromWbxml($response->getBody());
         $xpath = $this->xpath($dom);
 
         $this->assertSame('1', $xpath->query("//ns:FolderDelete/ns:Status")->item(0)->nodeValue);
         $this->assertSame(strval(++$params['SyncKey']), $xpath->query("//ns:FolderDelete/ns:SyncKey")->item(0)->nodeValue);
 
         // Note: After FolderDelete there are no changes in the following FolderSync expected
 
         // TODO: Assert the folders no longer exist
     }
 }