Add import, update What's New, add test, and fix comments

docs/iris/src/whatsnew/contributions_2.0/incompatiblechange_2017-Aug-29_fill_value_save_arg.txt

@@ -1 +1 @@
-* When saving a cube or list of cubes, a fill value or list of fill values can be specified via a new `fill_value` argument. If a list is supplied, each fill value will be applied to each cube in turn. If a `fill_value` argument is not specified, the default fill value for the file format and the cube's data type will be used. Fill values are no longer taken from the cube's `data` attribute when it is a masked array.
+* When saving a cube or list of cubes in netCDF, a fill value or list of fill values can be specified via a new `fill_value` argument. If a list is supplied, each fill value will be applied to each cube in turn. If a `fill_value` argument is not specified, the default fill value for the file format and the cube's data type will be used. Fill values are no longer taken from the cube's `data` attribute when it is a masked array.

lib/iris/fileformats/netcdf.py

@@ -48,6 +48,7 @@
 from iris.aux_factory import HybridHeightFactory, HybridPressureFactory, \
     OceanSigmaZFactory, OceanSigmaFactory, OceanSFactory, OceanSg1Factory, \
     OceanSg2Factory
+import iris.config
 import iris.coord_systems
 import iris.coords
 import iris.cube

lib/iris/tests/unit/fileformats/netcdf/test_Saver.py

@@ -413,7 +413,8 @@ def test_mask_lazy_fill_value(self):
             self.assertTrue(var[index].mask)
 
     def test_mask_lazy_default_fill_value(self):
-        # Test that masked lazy data saves correctly when given a fill value.
+        # Test that masked lazy data saves correctly using the default fill
+        # value.
         index = (1, 1)
         cube = self._make_cube('>f4', masked_index=index, lazy=True)
         with self._netCDF_var(cube) as var:
@@ -477,6 +478,15 @@ def test_masked_byte_default_fill_value(self):
             with self._netCDF_var(cube):
                 pass
 
+    def test_masked_byte_fill_value_passed(self):
+        # Test that no warning is raised when saving masked byte data with a
+        # fill value supplied if the the data does not contain the fill_value.
+        fill_value = 100
+        cube = self._make_cube('>i1', masked_value=2)
+        with self._warning_check('contains masked byte data', False):
+            with self._netCDF_var(cube, fill_value=fill_value):
+                pass
+
 
 class _Common__check_attribute_compliance(object):
     def setUp(self):

lib/iris/tests/unit/fileformats/netcdf/test_save.py

@@ -158,7 +158,7 @@ def test_None(self):
                 self.assertIs(None, kwargs['fill_value'])
 
     def test_single(self):
-        # Test that when a signle value is passed as the fill_value argument,
+        # Test that when a single value is passed as the fill_value argument,
         # that value is passed to each call to Saver.write
         cubes = self._make_cubes()
         fill_value = 12345.