add test that was previously failing

Author: GuySten

tests/unit_tests/test_geometry.py

@@ -403,3 +403,30 @@ def test_redundant_surfaces():
     geom = openmc.Geometry([c3])
     redundant_surfs = geom.remove_redundant_surfaces()
     assert len(redundant_surfs) == 0
+    
+
+def test_sphere_overlap(run_in_tmpdir):
+    model = openmc.model.Model() 
+    shell_material = openmc.Material()
+    shell_material.add_element("Au", 1.0, percent_type="ao")
+    shell_material.set_density("g/cm3", 1930) # revolver density
+    model.materials = openmc.Materials([shell_material])
+    surface_inner_shell = openmc.Sphere(r=0.0035)
+    surface_outer_shell = openmc.Sphere(r=0.0095)
+    sphere_surface_detector_1 = openmc.Sphere(r=20000, boundary_type="vacuum")
+    fuel_region = -surface_inner_shell
+    shell_region = +surface_inner_shell & -surface_outer_shell
+    void_region_1 = +surface_outer_shell & -sphere_surface_detector_1
+    fuel_cell = openmc.Cell(region=fuel_region)
+    shell_cell = openmc.Cell(region=shell_region, fill=shell_material)
+    void_cell_1 = openmc.Cell(region=void_region_1)
+    
+    model.geometry = openmc.Geometry([fuel_cell, shell_cell, void_cell_1])
+    source = openmc.Source()
+    source.angle = openmc.stats.Isotropic()
+    model.settings = openmc.Settings()
+    model.settings.batches = 100
+    model.settings.particles = 80000
+    model.settings.run_mode = "fixed source"
+    model.settings.source = source
+    model.run(geometry_debug=True)