diff --git a/log_enhancer/tests/test_core.py b/log_enhancer/tests/test_core.py
new file mode 100644
index 0000000..e879269
--- /dev/null
+++ b/log_enhancer/tests/test_core.py
@@ -0,0 +1,70 @@
+import pytest
+from typing import List, Dict
+
+import sys
+from pathlib import Path
+
+import importlib
+
+# Sicherstellen, dass src im Pfad ist
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.append(str(ROOT / 'src'))
+
+# Modulimport
+core = importlib.import_module('log_enhancer.core')
+
+
+def test_enhance_log_entries_adds_missing_fields():
+    sample_logs: List[Dict] = [
+        {"message": "Artifact processed successfully."},
+        {
+            "message": "Missing key.",
+            "expected_artifact_path": "/data/artifacts/x.json",
+        },
+    ]
+
+    enhanced = core.enhance_log_entries(sample_logs)
+
+    assert isinstance(enhanced, list)
+    assert all(isinstance(entry, dict) for entry in enhanced)
+
+    for entry in enhanced:
+        assert 'message' in entry and isinstance(entry['message'], str)
+        assert 'expected_artifact_path' in entry
+        assert 'artifact_key' in entry
+
+    # Eingaben, die bereits pfade enthalten, sollten beibehalten werden
+    for original, result in zip(sample_logs, enhanced):
+        if 'expected_artifact_path' in original:
+            assert result['expected_artifact_path'] == original['expected_artifact_path']
+
+
+def test_enhance_log_entries_preserves_length():
+    logs = [{"message": f"msg-{i}"} for i in range(3)]
+    result = core.enhance_log_entries(logs)
+    assert len(result) == len(logs)
+
+
+def test_enhance_log_entries_handles_empty_list():
+    assert core.enhance_log_entries([]) == []
+
+
+def test_enhance_log_entries_invalid_input_type():
+    with pytest.raises(AssertionError):
+        core.enhance_log_entries("not a list")
+
+
+def test_enhance_log_entries_field_validation():
+    logs = [{"message": None}]  # invalid type
+    with pytest.raises(AssertionError):
+        core.enhance_log_entries(logs)
+
+
+def test_enhance_log_entries_fills_consistent_values():
+    logs = [{"message": "Processing unknown artifact."}]
+    result = core.enhance_log_entries(logs)
+
+    entry = result[0]
+    assert entry['message'] == "Processing unknown artifact."
+    assert entry['expected_artifact_path'].startswith("/unknown/") or entry['expected_artifact_path'] != ''
+    assert len(entry['artifact_key']) > 0
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