diff --git a/fft_analysis/tests/test_io_utils.py b/fft_analysis/tests/test_io_utils.py
new file mode 100644
index 0000000..159c8d8
--- /dev/null
+++ b/fft_analysis/tests/test_io_utils.py
@@ -0,0 +1,76 @@
+import json
+import os
+import tempfile
+import numpy as np
+import pytest
+from pathlib import Path
+
+from fft_analysis import io_utils
+
+
+def test_load_audio_file_wav(monkeypatch):
+    # Mock scipy.io.wavfile.read to return synthetic data
+    import scipy.io.wavfile as wavfile
+
+    sample_rate = 44100
+    data = np.array([0, 32767, -32768], dtype=np.int16)
+
+    def mock_read(file_path):
+        assert isinstance(file_path, (str, Path))
+        return sample_rate, data
+
+    monkeypatch.setattr(wavfile, 'read', mock_read)
+
+    arr, sr = io_utils.load_audio_file("dummy.wav")
+    assert isinstance(arr, np.ndarray)
+    assert sr == sample_rate
+    assert np.allclose(arr, data.astype(np.float32) / np.max(np.abs(data)))
+
+
+def test_load_audio_file_invalid_path():
+    with pytest.raises(FileNotFoundError):
+        io_utils.load_audio_file("nonexistent_path.wav")
+
+
+def test_save_spectrum_to_json_and_verify(tmp_path):
+    spectrum = np.array([0.1, 0.5, 0.9, 0.2])
+    output_file = tmp_path / "spectrum.json"
+
+    io_utils.save_spectrum_to_json(spectrum, str(output_file))
+
+    assert output_file.exists()
+
+    with open(output_file, "r", encoding="utf-8") as f:
+        data = json.load(f)
+
+    assert isinstance(data, dict)
+    assert 'frequencies' in data and 'magnitudes' in data
+    assert isinstance(data['frequencies'], list)
+    assert isinstance(data['magnitudes'], list)
+    assert len(data['frequencies']) == len(data['magnitudes']) == len(spectrum)
+
+
+def test_save_spectrum_to_json_invalid_path():
+    spectrum = np.array([0.1, 0.2, 0.3])
+    invalid_path = "/invalid_directory/output.json"
+
+    with pytest.raises((OSError, IOError)):
+        io_utils.save_spectrum_to_json(spectrum, invalid_path)
+
+
+def test_load_audio_file_normalization(monkeypatch):
+    import scipy.io.wavfile as wavfile
+
+    sample_rate = 48000
+    data = np.array([0, 1000, -1000], dtype=np.int16)
+
+    def mock_read(file_path):
+        return sample_rate, data
+
+    monkeypatch.setattr(wavfile, 'read', mock_read)
+
+    arr, sr = io_utils.load_audio_file("file.wav")
+
+    assert sr == sample_rate
+    assert np.isclose(np.max(arr), 1.0, atol=0.01) or np.isclose(np.max(arr), 0.0)
+    assert np.isclose(np.min(arr), -1.0, atol=0.01) or np.isclose(np.min(arr), 0.0)