diff --git a/frozen_runs_analysis/tests/test_core.py b/frozen_runs_analysis/tests/test_core.py
new file mode 100644
index 0000000..d6edecc
--- /dev/null
+++ b/frozen_runs_analysis/tests/test_core.py
@@ -0,0 +1,64 @@
+import pytest
+import pandas as pd
+from typing import List, Dict
+from frozen_runs_analysis import core
+
+class DummyRunData:
+    def __init__(self, run_id: str, status: str, sanity_checks: Dict[str, float], config_hash: str):
+        self.run_id = run_id
+        self.status = status
+        self.sanity_checks = sanity_checks
+        self.config_hash = config_hash
+
+@pytest.fixture
+def sample_runs() -> List[DummyRunData]:
+    return [
+        DummyRunData(run_id="#24", status="pinned", sanity_checks={"missing_pairs": 1, "clock_switch": 0}, config_hash="abc123"),
+        DummyRunData(run_id="#25", status="unpinned", sanity_checks={"missing_pairs": 2, "clock_switch": 1}, config_hash="abc123"),
+        DummyRunData(run_id="#26", status="pinned", sanity_checks={"missing_pairs": 0, "clock_switch": 0}, config_hash="def456"),
+        DummyRunData(run_id="#27", status="unpinned", sanity_checks={"missing_pairs": 3, "clock_switch": 2}, config_hash="abc123"),
+    ]
+
+@pytest.fixture
+def sample_dataframe(sample_runs):
+    df = pd.DataFrame([
+        {"run_id": r.run_id, "status": r.status, "missing_pairs": r.sanity_checks["missing_pairs"], "clock_switch": r.sanity_checks["clock_switch"], "config_hash": r.config_hash}
+        for r in sample_runs
+    ])
+    return df
+
+@pytest.mark.parametrize("input_data_type", [list, pd.DataFrame])
+def test_analyse_frozen_runs_output_type(sample_runs, sample_dataframe, input_data_type):
+    data = sample_runs if input_data_type is list else sample_dataframe
+    result = core.analyse_frozen_runs(data)
+    assert isinstance(result, dict)
+    assert "flip_flop_frequency" in result
+    assert "hash_stability" in result
+    assert "p95_sanity_missing_pairs" in result
+
+
+@pytest.mark.parametrize("edge_case_runs", [
+    [],  # Empty list
+    [DummyRunData(run_id="#1", status="pinned", sanity_checks={}, config_hash="xyz")],  # Minimal fields
+])
+def test_analyse_frozen_runs_edge_cases(edge_case_runs):
+    result = core.analyse_frozen_runs(edge_case_runs)
+    assert isinstance(result, dict)
+    assert set(result.keys()) >= {"flip_flop_frequency", "hash_stability", "p95_sanity_missing_pairs"}
+
+
+def test_analyse_frozen_runs_reproducibility(sample_runs):
+    result1 = core.analyse_frozen_runs(sample_runs)
+    result2 = core.analyse_frozen_runs(sample_runs)
+    assert result1 == result2, "Analyseergebnisse müssen deterministisch und reproduzierbar sein"
+
+
+def test_analyse_frozen_runs_statistical_sanity(sample_runs):
+    result = core.analyse_frozen_runs(sample_runs)
+    flip_flop = result.get("flip_flop_frequency", None)
+    assert 0 <= flip_flop <= 1, "Flip-Flop-Frequenz muss zwischen 0 und 1 liegen"
+    p95_missing = result.get("p95_sanity_missing_pairs", 0)
+    assert isinstance(p95_missing, (int, float)) and p95_missing >= 0
+    hash_stability = result.get("hash_stability", {})
+    assert isinstance(hash_stability, dict)
+    assert all(isinstance(k, str) and isinstance(v, int) for k, v in hash_stability.items())
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