diff --git a/rollout_report_generator/tests/test_core.py b/rollout_report_generator/tests/test_core.py
new file mode 100644
index 0000000..89b094a
--- /dev/null
+++ b/rollout_report_generator/tests/test_core.py
@@ -0,0 +1,68 @@
+import io
+import tempfile
+from pathlib import Path
+import pandas as pd
+import pytest
+
+from src.rollout_report_generator import core
+
+def _create_sample_csv(tmp_path: Path) -> Path:
+    data = pd.DataFrame(
+        [
+            {"unknown_rate": 0.02, "warn_rate": 0.03, "policy_hash": "abc123", "runs": 10},
+            {"unknown_rate": 0.05, "warn_rate": 0.08, "policy_hash": "def456", "runs": 12},
+            {"unknown_rate": 0.01, "warn_rate": 0.02, "policy_hash": "ghi789", "runs": 9},
+            {"unknown_rate": 0.10, "warn_rate": 0.15, "policy_hash": "xyz000", "runs": 7},
+        ]
+    )
+    csv_path = tmp_path / "rollout_series.csv"
+    data.to_csv(csv_path, index=False)
+    return csv_path
+
+
+def test_generate_report_creates_markdown_file(tmp_path: Path):
+    csv_file = _create_sample_csv(tmp_path)
+    md_file = tmp_path / "report.md"
+
+    core.generate_report(str(csv_file), str(md_file))
+
+    assert md_file.exists(), "Markdown file should be created."
+    content = md_file.read_text().strip()
+
+    assert len(content) > 0, "Markdown content should not be empty."
+    assert "unknown_rate" in content
+    assert "warn_rate" in content
+    assert "Median" in content or "median" in content
+
+
+def test_generate_report_with_invalid_csv_raises(tmp_path: Path):
+    invalid_csv = tmp_path / "invalid.csv"
+    invalid_csv.write_text("not,a,valid,csv\n1,2,3")
+    md_file = tmp_path / "report.md"
+
+    with pytest.raises(Exception):
+        core.generate_report(str(invalid_csv), str(md_file))
+
+
+def test_generate_report_empty_csv(tmp_path: Path):
+    empty_csv = tmp_path / "empty.csv"
+    pd.DataFrame(columns=["unknown_rate", "warn_rate", "policy_hash", "runs"]).to_csv(empty_csv, index=False)
+    out_md = tmp_path / "report.md"
+
+    core.generate_report(str(empty_csv), str(out_md))
+
+    content = out_md.read_text()
+    assert "No data" in content or len(content) > 0
+
+
+def test_generate_report_statistics_are_correct(tmp_path: Path):
+    csv_file = _create_sample_csv(tmp_path)
+    out_md = tmp_path / "report.md"
+
+    core.generate_report(str(csv_file), str(out_md))
+    content = out_md.read_text()
+
+    # Check that numeric summaries exist in Markdown report
+    assert any(term in content for term in ["min", "p95", "max"])
+    assert "policy_hash" in content
+    assert "runs" in content
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