Add test report documentation

docs/source/testing.rst

@@ -88,3 +88,13 @@ changed.
 Test Reports
 ++++++++++++
 
+Test reports are automatically generated when building documentation
+from all xml report files found in sub-directories of the artifact
+directory.
+
+.. note::
+
+    Please make sure to not commit any additional files into the
+    `test_rsts subfolder? of this documentation. Also, do not commit
+    `test_results.rst`; it is autogenerated.
+