Add test for openmc.lib.sample_external_source

tests/unit_tests/test_lib.py

@@ -807,3 +807,44 @@ def test_cell_rotation(pincell_model_w_univ, mpi_intracomm):
     cell.rotation = (180., 0., 0.)
     assert cell.rotation == pytest.approx([180., 0., 0.])
     openmc.lib.finalize()
+
+
+def test_sample_external_source(run_in_tmpdir, mpi_intracomm):
+    # Define a simple model and export
+    mat = openmc.Material()
+    mat.add_nuclide('U235', 1.0e-2)
+    sph = openmc.Sphere(r=100.0, boundary_type='vacuum')
+    cell = openmc.Cell(fill=mat, region=-sph)
+    model = openmc.Model()
+    model.geometry = openmc.Geometry([cell])
+    model.settings.source = openmc.Source(
+        space=openmc.stats.Box([-5., -5., -5.], [5., 5., 5.]),
+        angle=openmc.stats.Monodirectional((0., 0., 1.)),
+        energy=openmc.stats.Discrete([1.0e5], [1.0])
+    )
+    model.settings.particles = 1000
+    model.settings.batches = 10
+    model.export_to_xml()
+
+    # Sample some particles and make sure they match specified source
+    openmc.lib.init()
+    particles = openmc.lib.sample_external_source(10, prn_seed=3)
+    for p in particles:
+        assert -5. < p.r[0] < 5.
+        assert -5. < p.r[1] < 5.
+        assert -5. < p.r[2] < 5.
+        assert p.u[0] == 0.0
+        assert p.u[1] == 0.0
+        assert p.u[2] == 1.0
+        assert p.E == 1.0e5
+
+    # Using the same seed should produce the same particles
+    other_particles = openmc.lib.sample_external_source(10, prn_seed=3)
+    for p1, p2 in zip(particles, other_particles):
+        assert p1.r == p2.r
+        assert p1.u == p2.u
+        assert p1.E == p2.E
+        assert p1.time == p2.time
+        assert p1.wgt == p2.wgt
+
+    openmc.lib.finalize()