test: bind Simulation usability guard on host doubles

tests/unit/test_jets.py

@@ -194,6 +194,7 @@ def test_public_surface_exchange_for_jet_preserves_aperture_at_zero_and_reverse(
     field, bodies = jet_case(device, [jet])
     sim = SimpleNamespace(bodies=bodies, field=field, _initialized=True,
                           stream=SimpleNamespace(synchronize=device.synchronize))
+    sim._require_usable = Simulation._require_usable.__get__(sim)
     cl = field.curved
     assert bodies.get(0).surface_actuation is None
     aperture, velocity = cl.aperture, cl.surface_velocity.copy()
@@ -218,6 +219,7 @@ def test_public_surface_exchange_keeps_legacy_and_passive_guards(device):
     bodies.sync_to_gpu(field)
     sim = SimpleNamespace(bodies=bodies, field=field,
                           stream=SimpleNamespace(synchronize=device.synchronize))
+    sim._require_usable = Simulation._require_usable.__get__(sim)
     for value in Simulation.read_surface_exchange(sim, 0).values():
         np.testing.assert_array_equal(value, 0.)
     field.curved.free_gpu_columns()