Temporary fix for bug that broke inactive TDC in Segment

cheetah/accelerator/transverse_deflecting_cavity.py

@@ -99,7 +99,8 @@ def is_active(self) -> bool:
 
     @property
     def is_skippable(self) -> bool:
-        return not self.is_active
+        # TODO: Implement drrift-like `transfer_map` and set to `self.is_active`
+        return False
 
     def track(self, incoming: Beam) -> Beam:
         """

tests/test_transverse_deflecting_cavity.py

@@ -133,3 +133,16 @@ def test_transverse_deflecting_cavity_all_parameters_vectorization():
     outgoing_beam = tdc.track(incoming_beam)
 
     assert outgoing_beam.particles.shape[:-2] == torch.Size([4, 3, 2, 2])
+
+
+def test_tracking_inactive_in_segment():
+    """
+    Test that tracking through a `Segment` that contains an inactive
+    `TransverseDeflectingCavity` does not throw an exception. This was an issue in #290.
+    """
+    segment = cheetah.Segment(
+        elements=[cheetah.TransverseDeflectingCavity(length=torch.tensor(1.0))]
+    )
+    beam = cheetah.ParticleBeam.from_parameters()
+
+    segment.track(beam)