Adding unit test for dlopen source

tests/unit_tests/dlopen_source/source_sampling.cpp

@@ -0,0 +1,23 @@
+#include <iostream>
+#include "openmc/random_lcg.h"
+#include "openmc/source.h"
+#include "openmc/particle.h"
+
+// you must have external C linkage here otherwise 
+// dlopen will not find the file
+extern "C" openmc::Particle::Bank sample_source() {
+    openmc::Particle::Bank particle;
+    // wgt
+    particle.particle = openmc::Particle::Type::neutron;
+    particle.wgt = 1.0;
+    // position
+    
+    particle.r.x = 0.;
+    particle.r.y = 0.;
+    particle.r.z = 0.;
+    // angle
+    particle.u = {1.,0,0};
+    particle.E = 14.08e6;
+    particle.delayed_group = 0;
+    return particle;    
+}

tests/unit_tests/dlopen_source/test_dlopen_source.py

@@ -0,0 +1,57 @@
+import openmc
+import pytest
+import os
+
+# compile the external source
+def compile_source():
+    # needs a more robust way to know where the
+    # Makefile is
+    status  = os.system('cp /usr/local/share/Makefile .')
+    assert os.WEXITSTATUS(status) == 0
+    status = os.system('make')
+    assert os.WEXITSTATUS(status) == 0
+    
+    return
+
+# build the test geometry
+def make_geometry():
+    mats = openmc.Materials()
+
+    natural_lead = openmc.Material(1, "natural_lead")
+    natural_lead.add_element('Pb', 1,'ao')
+    natural_lead.set_density('g/cm3', 11.34)
+    mats.append(natural_lead)
+
+    # surfaces
+    surface_sph1 = openmc.Sphere(r=100) 
+    volume_sph1 = -surface_sph1 
+    
+    # cell
+    cell_1 = openmc.Cell(region=volume_sph1)
+    cell_1.fill = natural_lead #assigning a material to a cell
+    universe = openmc.Universe(cells=[cell_1]) #hint, this list will need to include the new cell
+    geom = openmc.Geometry(universe)
+
+    # settings
+    sett = openmc.Settings()
+    batches = 10
+    sett.batches = batches
+    sett.inactive = 0
+    sett.particles = 1000
+    sett.particle = "neutron"
+    sett.run_mode = 'fixed source'
+
+    #source
+    source = openmc.Source()
+    source.library = PATH+'source_sampling.so'
+    sett.source = source
+
+    # run
+    model = openmc.model.Model(geom,mats,sett)
+    return model
+
+def test_dlopen_source():
+    compile_source()
+    model = make_geometry()
+    model.run()
+