diff --git a/tests/regression_tests/dagmc/external/test.py b/tests/regression_tests/dagmc/external/test.py
index 938e262ff..2671f9a84 100644
--- a/tests/regression_tests/dagmc/external/test.py
+++ b/tests/regression_tests/dagmc/external/test.py
@@ -101,15 +101,25 @@ class ExternalDAGMCTest(PyAPITestHarness):
         self.executable = executable
 
     def _run_openmc(self):
+    """
+    Just test if results generated with the external C++ API are
+    self-consistent with the internal python API.
+    We generate the "truth" results with the python API but
+    the main test produces the results file by running the
+    executable compiled from main.cpp. This future-proofs
+    the test - we only care that the two routes are equivalent.
+    """
         if config['update']:
             # Generate the results file with internal python API
             openmc.run(openmc_exec=config['exe'], event_based=config['event'])
         elif config['mpi']:
             mpi_args = [config['mpiexec'], '-n', config['mpi_np']]
+            # Run main cpp executable with MPI
             openmc.run(openmc_exec=self.executable,
                        mpi_args=mpi_args,
                        event_based=config['event'])
         else:
+            # Run main cpp executable
             openmc.run(openmc_exec=self.executable,
                        event_based=config['event'])