diff --git a/unknowns_classifier/tests/test_core.py b/unknowns_classifier/tests/test_core.py
new file mode 100644
index 0000000..2696958
--- /dev/null
+++ b/unknowns_classifier/tests/test_core.py
@@ -0,0 +1,34 @@
+import pytest
+from unknowns_classifier import core
+
+@pytest.fixture
+def sample_unknowns():
+    return [
+        {"message": "Schema mismatch detected in run A"},
+        {"message": "Missing artifact: model.pkl"},
+        {"message": "Schema mismatch in run B"},
+        {"message": "Unknown artifact missing: data.csv"},
+    ]
+
+def test_classify_unknowns_nominal(sample_unknowns):
+    results = core.classify_unknowns(sample_unknowns)
+    assert isinstance(results, list)
+    assert all(isinstance(r, core.UnknownClassification) for r in results)
+
+    types = [r.unknown_type for r in results]
+    counts = {r.unknown_type: r.count for r in results}
+
+    assert "schema_mismatch" in types
+    assert "artefakt_fehlt" in types
+
+    assert counts["schema_mismatch"] == 2
+    assert counts["artefakt_fehlt"] == 2
+
+def test_classify_unknowns_empty():
+    results = core.classify_unknowns([])
+    assert isinstance(results, list)
+    assert len(results) == 0
+
+def test_classify_unknowns_invalid_input():
+    with pytest.raises((TypeError, KeyError)):
+        core.classify_unknowns(["not_a_dict", None, 123])