diff --git a/tests/conftest.py b/tests/conftest.py
index 55aba02..58a85cf 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -32,3 +32,11 @@ def simplified(
     polygon: list[tuple[float, float]], method: ReductionMethod
 ) -> list[tuple[float, float]]:
     return reduce_polygon(polygon, ReductionMode.EPSILON, 1e-6, method)
+
+
+@fixture(scope="class")
+@parametrize_with_cases("method", cases=".method_cases", scope="class")
+def simplified_len(
+    polygon: list[tuple[float, float]], method: ReductionMethod
+) -> list[tuple[float, float]]:
+    return reduce_polygon(polygon, ReductionMode.LENGTH, 100, method)
diff --git a/tests/test_integration.py b/tests/test_integration.py
index ebacacf..d250213 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -69,3 +69,36 @@ def test_containment(
         # The null polygon cannot contain itself
         if length:
             assert simplified_shapely.contains(original_shapely)
+
+    def test_len(
+        self,
+        polygon: list[tuple[float, float]],
+        simplified_len: list[tuple[float, float]],
+    ):
+        """Ensure reduced polygon vertices are a subset of the originals."""
+        # if isinstance(polygon, ShapelyPolygon):
+        #     original_set = set(map(lambda v: tuple(v), list(polygon.exterior.coords)))
+        # else:
+        #     original_set = set(map(lambda v: tuple(v), polygon))
+        # simplified_set = set(map(lambda v: tuple(v), simplified_len))
+
+        # assert simplified_set <= original_set
+        assert len(simplified_len) <= 100
+
+    def test_containment_len(
+        self,
+        polygon: list[tuple[float, float]],
+        simplified_len: list[tuple[float, float]],
+    ):
+        """Ensure reduced polygons contain the original in their interior."""
+        original_shapely = ShapelyPolygon(polygon)
+        simplified_shapely = ShapelyPolygon(simplified_len)
+
+        if isinstance(polygon, ShapelyPolygon):
+            length = polygon.length
+        else:
+            length = len(polygon)
+
+        # The null polygon cannot contain itself
+        if length:
+            assert simplified_shapely.contains(original_shapely)