diff --git a/tests/unit/test_mouse.py b/tests/unit/test_mouse.py
index b2398bf..b674801 100644
--- a/tests/unit/test_mouse.py
+++ b/tests/unit/test_mouse.py
@@ -128,9 +128,17 @@ def test_no_sharp_turns_or_walls_near_endpoint() -> None:
             # Vertical wall: >=4 consecutive tail points within 2 px of
             # the target x while spanning >10 px of y.
             near_x = np.abs(tail[:, 0] - end[0]) <= 2.0
+            run_start = 0
             run = 0
-            for i, flag in enumerate(near_x[:-1]):  # exclude final point
-                run = run + 1 if flag else 0
-                assert run < 4 or np.ptp(tail[near_x][:, 1]) <= 10.0, (
-                    f"{start}->{end} seed={seed}: vertical wall at target x"
-                )
+            for j, flag in enumerate(near_x[:-1]):  # exclude final point
+                if flag:
+                    if run == 0:
+                        run_start = j
+                    run += 1
+                else:
+                    run = 0
+                if run >= 4:
+                    span = np.ptp(tail[run_start : j + 1, 1])
+                    assert span <= 10.0, (
+                        f"{start}->{end} seed={seed}: vertical wall at target x"
+                    )
diff --git a/tests/unit/test_postprocess.py b/tests/unit/test_postprocess.py
index c053a04..3bd1faa 100644
--- a/tests/unit/test_postprocess.py
+++ b/tests/unit/test_postprocess.py
@@ -199,3 +199,12 @@ def test_warp_endpoints_correction_local_to_each_end() -> None:
     f[0] = 0.08  # start residual only
     fo, _ = warp_endpoints(f, l)
     assert np.abs(fo[24:] - f[24:]).max() < 0.02
+
+
+def test_warp_endpoints_does_not_mutate_inputs() -> None:
+    f = np.linspace(0.05, 1.10, 32)
+    l = np.linspace(0.03, -0.07, 32)
+    f_orig, l_orig = f.copy(), l.copy()
+    warp_endpoints(f, l)
+    assert np.array_equal(f, f_orig)
+    assert np.array_equal(l, l_orig)