diff --git a/tests/upload-manager.test.js b/tests/upload-manager.test.js
index be64771..3b2717f 100644
--- a/tests/upload-manager.test.js
+++ b/tests/upload-manager.test.js
@@ -280,6 +280,86 @@ describe('UploadManager', () => {
     await assert.rejects(mgr._sleep(5000, ac.signal), /Aborted/);
   });
 
+  it('file not found produces descriptive error', async () => {
+    // Override fs.statSync to throw ENOENT for a specific path
+    const fs = require('fs');
+    const origStat = fs.statSync;
+    fs.statSync = function(p) {
+      if (p === '/test/deleted.mp4') throw Object.assign(new Error('ENOENT'), { code: 'ENOENT' });
+      return origStat.call(this, p);
+    };
+
+    const mgr = new UploadManager({});
+    const errors = [];
+    mgr.on('progress', (d) => { if (d.error) errors.push(d.error); });
+
+    await mgr.startBatch([
+      { file: '/test/deleted.mp4', hoster: 'doodstream.com', apiKey: 'key1' }
+    ]);
+
+    fs.statSync = origStat;
+    assert.ok(errors.some(e => e.includes('nicht gefunden')), `expected "nicht gefunden" error, got: ${errors.join(', ')}`);
+  });
+
+  it('zero-byte file produces descriptive error', async () => {
+    fakeFileSize = 0;
+
+    const mgr = new UploadManager({});
+    const errors = [];
+    mgr.on('progress', (d) => { if (d.error) errors.push(d.error); });
+
+    await mgr.startBatch([
+      { file: '/test/empty.mp4', hoster: 'doodstream.com', apiKey: 'key1' }
+    ]);
+
+    assert.ok(errors.some(e => e.includes('0 Bytes')), `expected "0 Bytes" error, got: ${errors.join(', ')}`);
+  });
+
+  it('empty batch completes immediately with zero counts', async () => {
+    const mgr = new UploadManager({});
+    let summary = null;
+    mgr.on('batch-done', (s) => { summary = s; });
+
+    const start = Date.now();
+    await mgr.startBatch([]);
+    const elapsed = Date.now() - start;
+
+    assert.ok(summary, 'batch-done should be emitted');
+    assert.equal(summary.total, 0);
+    assert.equal(summary.succeeded, 0);
+    assert.equal(summary.failed, 0);
+    assert.ok(elapsed < 200, `empty batch should complete fast, took ${elapsed}ms`);
+  });
+
+  it('scaleParallelUploads limits per-hoster count to global limit', async () => {
+    let concurrent = 0;
+    let maxConcurrent = 0;
+
+    mockUploadFile.mock.mockImplementation(async (hoster, filePath, apiKey, onProgress) => {
+      concurrent++;
+      maxConcurrent = Math.max(maxConcurrent, concurrent);
+      await new Promise(r => setTimeout(r, 40));
+      concurrent--;
+      if (onProgress) onProgress(fakeFileSize, fakeFileSize);
+      return { download_url: 'ok', embed_url: null, file_code: 'ok' };
+    });
+
+    const mgr = new UploadManager(
+      { 'doodstream.com': { retries: 0, parallelCount: 10, maxSpeedKbs: 0, restartBelowKbs: 0, timeIntervalSec: 0, maxSizeMb: 0 } },
+      { parallelUploadCount: 2, scaleParallelUploads: true }
+    );
+
+    await mgr.startBatch([
+      { file: '/test/a.mp4', hoster: 'doodstream.com', apiKey: 'k' },
+      { file: '/test/b.mp4', hoster: 'doodstream.com', apiKey: 'k' },
+      { file: '/test/c.mp4', hoster: 'doodstream.com', apiKey: 'k' },
+      { file: '/test/d.mp4', hoster: 'doodstream.com', apiKey: 'k' },
+      { file: '/test/e.mp4', hoster: 'doodstream.com', apiKey: 'k' }
+    ]);
+
+    assert.ok(maxConcurrent <= 2, `scaleParallelUploads should cap at 2, was ${maxConcurrent}`);
+  });
+
   it('stats event contains expected fields', async () => {
     // Make upload take long enough for stats interval to fire
     mockUploadFile.mock.mockImplementation(async (hoster, filePath, apiKey, onProgress, signal) => {