Add testing description

Author: xylar

design_docs/mpas_xarray_class.md

@@ -150,12 +150,32 @@ the `Time` coordinate to only include dates between `start_date` and
 
 <h1> Testing </h1>
 
-(This is as far as I got in the draft design doc. Testing will be added tomorrow.)
+<h2> Testing and Validation: MPAS-Analysis specific functionality should be supported in
+xarray preprossing <br>
+Date last modified: 2017/02/10 <br>
+Contributors: Xylar Asay-Davis
+</h2>
+
+In [xylar/MPAS-Analysis/variable_mapping_reorg](https://github.com/xylar/MPAS-Analysis/tree/variable_mapping_reorg),
+the unit testing for mpas_xarray has been updated.  This includes moving unit testing for
+variable mapping elsewhere.
+
+I have tested, to the extent that I am able, that the results of a G240km ACME test case
+are bit-for-bit identical to those from `develop`. (However, I'm having trouble on my
+laptop with `ncremap` giving me a fill-value related error.)
 
-<h2> Testing and Validation: short-desciption-of-testing-here <br>
-Date last modified: YYYY/MM/DD <br>
-Contributors: (add your name to this list if it does not appear)
+I will make sure all tests with config files in the `configs/lanl` directory produce
+bit-for-bit results with the current `develop`.
+
+<h2> Testing and Validation: MPAS-Analysis specific functionality should be supported in
+xarray preprossing <br>
+Date last modified: 2017/02/10 <br>
+Contributors: Xylar Asay-Davis
 </h2>
-How will XXX be tested, i.e., how will be we know when we have met requirement
-XXX? What testing will be included for use with `py.test` for continuous integration?
-Description of how testing that requires off-line or specialized setup will be used.
+
+Largely, the same as above.
+
+I have added unit testing for `MpasAnalysisXarray` (mostly via the standalone
+`dataset.utility.open_multifile_dataset` function).  These tests ensure that:
+  - variable mapping works as expected
+  - start and end dates work as expected