diff --git a/data_logging/tests/test_core.py b/data_logging/tests/test_core.py
new file mode 100644
index 0000000..9fa4f53
--- /dev/null
+++ b/data_logging/tests/test_core.py
@@ -0,0 +1,60 @@
+import pytest
+import csv
+from pathlib import Path
+from datetime import datetime
+from pydantic import ValidationError
+
+import sys
+import os
+
+# Sicherstellen, dass das src-Paket importiert werden kann
+ROOT_DIR = Path(__file__).resolve().parent.parent
+SRC_DIR = ROOT_DIR / 'src'
+sys.path.insert(0, str(SRC_DIR))
+
+from data_logging.core import LogEntry, log_data
+
+def make_sample_entries():
+    return [
+        LogEntry(timestamp=datetime(2024, 1, 1, 12, 0, 0), value=-0.5, status='valid'),
+        LogEntry(timestamp=datetime(2024, 1, 1, 12, 5, 0), value=-1.2, status='error')
+    ]
+
+def test_log_data_creates_csv_successfully(tmp_path: Path):
+    data = make_sample_entries()
+    output_file = tmp_path / 'test_log.csv'
+    success = log_data(data, str(output_file))
+
+    assert success is True
+    assert output_file.exists(), 'CSV wurde nicht erstellt'
+
+    with open(output_file, newline='') as f:
+        reader = csv.DictReader(f)
+        rows = list(reader)
+
+    assert len(rows) == len(data)
+    # Validieren von Feldern
+    for row, entry in zip(rows, data):
+        assert row['timestamp'] == entry.timestamp.isoformat()
+        assert float(row['value']) == pytest.approx(entry.value)
+        assert row['status'] == entry.status
+
+def test_log_entry_invalid_fields_raise_validation_error():
+    # Ungültiger Timestamp
+    with pytest.raises(ValidationError):
+        LogEntry(timestamp='not-a-date', value=-2.3, status='valid')
+    # Ungültiger Typ für Value
+    with pytest.raises(ValidationError):
+        LogEntry(timestamp=datetime.now(), value='NaN', status='valid')
+
+
+def test_log_data_handles_empty_list(tmp_path: Path):
+    output_file = tmp_path / 'empty.csv'
+    success = log_data([], str(output_file))
+    assert success is True
+    assert output_file.exists()
+    with open(output_file) as f:
+        content = f.read()
+    # Bei leerer Eingabe sollte nur Header geschrieben werden
+    assert 'timestamp' in content
+    assert content.count('\n') == 1
\ No newline at end of file