Adding a test for restart runs

tests/unit_tests/test_restart.py

@@ -0,0 +1,23 @@
+import openmc
+
+import pytest
+
+def test_restart(run_in_tmpdir):
+
+    pincell = openmc.examples.pwr_pin_cell()
+
+    # run the pincell
+    sp_file = pincell.run()
+
+    # run a restart with the resulting statepoint
+    # and the settings unchanged
+
+    with pytest.raises(RuntimeError, match='is smaller than the number of batches'):
+        pincell.run(restart_file=sp_file)
+
+    # update the number of batches and run again
+    pincell.settings.batches = 15
+    sp_file = pincell.run(restart_file=sp_file)
+
+    sp = openmc.StatePoint(sp_file)
+    assert sp.n_batches == 15