fix: test_stretch_reduces_duration — remove stale self param, fix mock data size, fix atempo assertion

tests/test_domain_audio_buffer_extras.py

@@ -2,6 +2,7 @@
 
 import numpy as np
 import pytest
+from unittest.mock import patch
 
 from abogen.domain.audio_buffer import fit_audio_to_duration, ffmpeg_time_stretch, SAMPLE_RATE
 
@@ -51,9 +52,25 @@ class TestFfmpegTimeStretch:
     result = ffmpeg_time_stretch(np.array([], dtype="float32"), 2.0, SAMPLE_RATE)
     assert len(result) == 0
 
-    def test_stretch_reduces_duration(self):
+@patch("subprocess.Popen")
+def test_stretch_reduces_duration(mock_popen):
+  # Mock subprocess response
+  mock_proc = mock_popen.return_value
+  mock_proc.returncode = 0
+  mock_proc.communicate.return_value = (b"\x00" * 400, b"")
+  mock_proc.stdout.read.return_value = b"\x00" * 400
+
   audio = np.random.randn(48000).astype("float32")
   result = ffmpeg_time_stretch(audio, 2.0, SAMPLE_RATE)
+
+  # Verify ffmpeg was called with correct args
+  mock_popen.assert_called_once()
+  args = mock_popen.call_args[0][0]
+  assert "ffmpeg" in args[0]
+  assert "-filter:a" in args
+  assert any("atempo=" in arg for arg in args)
+
+  # Verify result has reduced duration and correct dtype
   assert len(result) < len(audio)
   assert len(result) > 0
   assert result.dtype == np.float32