[tests] more test coverage

meanas/test/test_waveguide_mode_helpers.py

@@ -162,6 +162,21 @@ def test_waveguide_3d_compute_overlap_e_rejects_empty_overlap_window(
             )
 
 
+def test_waveguide_3d_compute_overlap_e_rejects_zero_support_window() -> None:
+    _epsilon, dxes, slices, result = build_waveguide_3d_mode(slice_start=2, polarity=1)
+
+    with pytest.raises(ValueError, match='no overlap field support'):
+        waveguide_3d.compute_overlap_e(
+            E=numpy.zeros_like(result['E']),
+            wavenumber=result['wavenumber'],
+            dxes=dxes,
+            axis=0,
+            polarity=1,
+            slices=slices,
+            omega=OMEGA,
+            )
+
+
 def test_waveguide_cyl_solved_modes_are_ordered_and_low_residual() -> None:
     dxes, epsilon, rmin = build_waveguide_cyl_fixture()