diff --git a/dry_run_mode/tests/test_core.py b/dry_run_mode/tests/test_core.py
new file mode 100644
index 0000000..decb5b9
--- /dev/null
+++ b/dry_run_mode/tests/test_core.py
@@ -0,0 +1,57 @@
+import pytest
+import types
+
+from dry_run_mode import core
+
+
+@pytest.fixture
+def sample_drift_report():
+    # Simulated drift report with pinned and unpinned strata
+    return {
+        'strata': [
+            {'stratum': 'pinned_alpha_low', 'alpha': 0.1, 'offset': 0, 'metrics': {'drift': 0.05}},
+            {'stratum': 'pinned_alpha_high', 'alpha': 0.3, 'offset': 0, 'metrics': {'drift': 0.25}},
+            {'stratum': 'unpinned_positive', 'alpha': 0.1, 'offset': 1.0, 'metrics': {'drift': 0.15}},
+            {'stratum': 'missing_metrics', 'alpha': 0.2, 'offset': 0, 'metrics': {}},
+        ]
+    }
+
+
+def test_dry_run_evaluation_basic(sample_drift_report):
+    result = core.dry_run_evaluation(sample_drift_report)
+    assert isinstance(result, dict)
+    assert 'results' in result
+    assert isinstance(result['results'], list)
+
+    expected_strata = {s['stratum'] for s in sample_drift_report['strata']}
+    actual_strata = {r['stratum'] for r in result['results']}
+    assert expected_strata == actual_strata
+
+
+def test_each_result_has_required_fields(sample_drift_report):
+    result = core.dry_run_evaluation(sample_drift_report)
+    for entry in result['results']:
+        assert {'stratum', 'dry_decision', 'reason'} <= set(entry.keys())
+        assert isinstance(entry['stratum'], str)
+        assert isinstance(entry['dry_decision'], str)
+        assert isinstance(entry['reason'], str)
+
+
+def test_reason_contains_keywords(sample_drift_report):
+    result = core.dry_run_evaluation(sample_drift_report)
+    for entry in result['results']:
+        # Reason should mention threshold or drift or missing data
+        reason = entry['reason'].lower()
+        assert any(k in reason for k in ['threshold', 'drift', 'missing', 'offset'])
+
+
+def test_invalid_input_type_raises():
+    with pytest.raises((AssertionError, TypeError, KeyError)):
+        core.dry_run_evaluation('not_a_dict')
+
+
+def test_handles_empty_report():
+    empty_report = {'strata': []}
+    result = core.dry_run_evaluation(empty_report)
+    assert isinstance(result, dict)
+    assert result['results'] == []
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