diff --git a/python_analysis_script/tests/test_core.py b/python_analysis_script/tests/test_core.py
new file mode 100644
index 0000000..92ec583
--- /dev/null
+++ b/python_analysis_script/tests/test_core.py
@@ -0,0 +1,57 @@
+import pytest
+import pandas as pd
+from pathlib import Path
+from datetime import datetime
+
+import src.python_analysis_script.core as core
+
+
+@pytest.fixture
+def sample_csv(tmp_path: Path) -> Path:
+    data = pd.DataFrame([
+        {"timestamp": datetime.now().isoformat(), "margin": 0.15, "flaky_flag": False, "subset_flip_count": 0, "mischfenster_p95": 0.9, "decision": ""},
+        {"timestamp": datetime.now().isoformat(), "margin": 0.05, "flaky_flag": False, "subset_flip_count": 1, "mischfenster_p95": 0.8, "decision": ""},
+        {"timestamp": datetime.now().isoformat(), "margin": -0.2, "flaky_flag": True, "subset_flip_count": 2, "mischfenster_p95": 0.5, "decision": ""}
+    ])
+    file_path = tmp_path / "sample.csv"
+    data.to_csv(file_path, index=False)
+    return file_path
+
+
+def test_analyze_backtest_returns_decisionresult_list(sample_csv: Path):
+    results = core.analyze_backtest(str(sample_csv))
+    assert isinstance(results, list)
+    assert all(isinstance(r, core.DecisionResult) for r in results)
+
+
+def test_decision_fields_are_valid(sample_csv: Path):
+    results = core.analyze_backtest(str(sample_csv))
+    for res in results:
+        assert res.decision in {"PASS", "WARN", "FAIL"}
+        assert isinstance(res.margin, float)
+        assert isinstance(res.flaky_flag, bool)
+        assert isinstance(res.subset_flip_count, int)
+        assert isinstance(res.mischfenster_p95, float)
+        assert isinstance(res.timestamp, datetime)
+
+
+def test_analyze_backtest_handles_empty_file(tmp_path: Path):
+    empty_file = tmp_path / "empty.csv"
+    pd.DataFrame(columns=["timestamp", "margin", "flaky_flag", "subset_flip_count", "mischfenster_p95", "decision"]).to_csv(empty_file, index=False)
+    results = core.analyze_backtest(str(empty_file))
+    assert isinstance(results, list)
+    assert len(results) == 0
+
+
+def test_policy_decision_logic_varies_with_margin(sample_csv: Path):
+    results = core.analyze_backtest(str(sample_csv))
+    margins = [r.margin for r in results]
+    decisions = [r.decision for r in results]
+    # There should be some differentiation between PASS/WARN/FAIL cases
+    unique_decisions = set(decisions)
+    assert len(unique_decisions) >= 2, "Expected mixed PASS/WARN/FAIL decisions based on margin values."
+
+
+def test_input_validation_with_missing_file():
+    with pytest.raises((FileNotFoundError, OSError)):
+        core.analyze_backtest("nonexistent_file.csv")