diff --git a/tests/test_clean.py b/tests/test_clean.py
index 03c7598..96b6900 100644
--- a/tests/test_clean.py
+++ b/tests/test_clean.py
@@ -21,3 +21,12 @@ def test_cast_types():
     df = pd.DataFrame({"count": ["1", "2", "3"]})
     result = cast_types(df, {"count": int})
     assert result["count"].dtype == int
+
+
+def test_strip_pii_hashes_values():
+    import hashlib
+    df = pd.DataFrame({"email": ["alice@example.com"]})
+    from src.transform.clean import strip_pii
+    result = strip_pii(df, ["email"])
+    expected = hashlib.sha256(b"alice@example.com").hexdigest()
+    assert result["email"].values[0] == expected