diff --git a/tests/scripts/test_audit_anomalies.py b/tests/scripts/test_audit_anomalies.py
new file mode 100644
index 000000000..b6acf3fde
--- /dev/null
+++ b/tests/scripts/test_audit_anomalies.py
@@ -0,0 +1,48 @@
+from typing import Optional
+
+import pytest
+
+from scripts.audit.anomalies import (
+    PropertyAudit,
+    _effective_lodged_divergence,
+)
+
+
+def _make_audit(
+    *,
+    lodged_sap: Optional[float],
+    effective_sap: Optional[float],
+    rebaseline_reason: str = "both",
+) -> PropertyAudit:
+    return PropertyAudit(
+        property_id=1,
+        uprn=None,
+        portfolio_id=796,
+        scenario_id=None,
+        scenario_goal_band=None,
+        lodged_sap=lodged_sap,
+        lodged_band=None,
+        effective_sap=effective_sap,
+        effective_band=None,
+        rebaseline_reason=rebaseline_reason,
+        post_sap=None,
+        post_band=None,
+        cost_of_works=None,
+        energy_bill_savings=None,
+        energy_consumption_savings=None,
+        solar_sap_points=None,
+        solar_bill_savings=None,
+        n_measures=0,
+    )
+
+
+class TestEffectiveLodgedDivergence:
+    def test_silent_when_lodged_sap_below_floor(self) -> None:
+        # Arrange — Class C exemplar: lodged=1, effective=76 (gap +75, but lodged is implausible upstream data)
+        audit = _make_audit(lodged_sap=1.0, effective_sap=76.0)
+
+        # Act
+        result = _effective_lodged_divergence(audit)
+
+        # Assert
+        assert result is None