diff --git a/inn_listen/tests/test_core.py b/inn_listen/tests/test_core.py
new file mode 100644
index 0000000..536e044
--- /dev/null
+++ b/inn_listen/tests/test_core.py
@@ -0,0 +1,82 @@
+import pytest
+import numpy as np
+from unittest.mock import patch, MagicMock
+from datetime import datetime
+from pathlib import Path
+import json
+
+import sys
+import logging
+
+# Importiere das zu testende Modul
+import inn_listen.core as core
+
+@pytest.fixture
+def synthetic_signal():
+    # Erzeugt ein synthetisches 50Hz-Signal mit Rauschen
+    fs = 1000
+    t = np.linspace(0, 1, fs, endpoint=False)
+    signal = np.sin(2 * np.pi * 50 * t) + 0.01 * np.random.randn(fs)
+    return signal
+
+@pytest.fixture
+def mock_audio_data(tmp_path):
+    return {
+        "timestamp": datetime.utcnow().isoformat(),
+        "frequency": 123.4,
+        "amplitude": 0.56,
+        "pattern": "harmonic"
+    }
+
+def test_start_stream_nominal(monkeypatch):
+    # Mock sounddevice.Stream
+    mock_stream = MagicMock()
+    monkeypatch.setattr(core, "sd", MagicMock(Stream=MagicMock(return_value=mock_stream)))
+
+    log_output = core.start_stream("contact", -12.0, 1024)
+    assert isinstance(log_output, str)
+    assert "contact" in log_output or "Audio" in log_output
+
+
+def test_start_stream_invalid_types():
+    # Überprüft Typvalidierung
+    with pytest.raises((TypeError, ValueError)):
+        core.start_stream(123, "invalid", "fft")
+
+
+def test_notch_filter_removes_frequency(synthetic_signal):
+    # Führt den Filter aus und überprüft, dass nicht identisch
+    filtered = core.notch_filter(synthetic_signal, freq=50.0, Q=30.0)
+    assert isinstance(filtered, np.ndarray)
+    assert filtered.shape == synthetic_signal.shape
+    diff_energy = np.sum(np.abs(filtered - synthetic_signal))
+    assert diff_energy > 0.0
+
+
+def test_notch_filter_invalid_inputs():
+    with pytest.raises((TypeError, ValueError)):
+        core.notch_filter("not-an-array", 50.0, 30.0)
+
+
+def test_audio_data_json_serialization(mock_audio_data, tmp_path):
+    output_file = tmp_path / "analysis.json"
+    with open(output_file, "w", encoding="utf-8") as fp:
+        json.dump(mock_audio_data, fp)
+    # Validate structure
+    with open(output_file, "r", encoding="utf-8") as fp:
+        restored = json.load(fp)
+    for field in ["timestamp", "frequency", "amplitude", "pattern"]:
+        assert field in restored
+    assert isinstance(restored["pattern"], str)
+
+
+def test_cli_invocation(monkeypatch):
+    mock_start_stream = MagicMock(return_value="Stream started")
+    monkeypatch.setattr(core, "start_stream", mock_start_stream)
+
+    test_args = ["prog", "--mic", "contact", "--gain", "-12.0", "--fft", "2048"]
+    monkeypatch.setattr(sys, "argv", test_args)
+    with patch("builtins.print") as mock_print:
+        core.main()
+    mock_start_stream.assert_called_once()
+    mock_print.assert_called()