removed cell measure mask check and error (#5181)

* removed cell measure mask check and error

* updated whatsnew

* updated tests

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* remove redundant test class in test_Saver.py, and its reference in test_Saver__lazy.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

docs/src/whatsnew/latest.rst

@@ -46,6 +46,10 @@ This document explains the changes made to Iris for this release
 #. `@trexfeathers`_ and `@pp-mo`_ made Iris' use of the `netCDF4`_ library
    thread-safe. (:pull:`5095`)
 
+#. `@ESadek-MO`_ removed check and error raise for saving
+   cubes with masked :class:`iris.coords.CellMeasure`.
+   (:issue:`5147`, :pull:`5181`)
+
 
 💣 Incompatible Changes
 =======================

lib/iris/fileformats/netcdf/saver.py

@@ -1933,16 +1933,6 @@ def _create_generic_cf_array_var(
             # Check if this is a dim-coord.
             is_dimcoord = cube is not None and element in cube.dim_coords
 
-            if isinstance(element, iris.coords.CellMeasure):
-                # Disallow saving of *masked* cell measures.
-                # NOTE: currently, this is the only functional difference in
-                # variable creation between an ancillary and a cell measure.
-                if iris.util.is_masked(data):
-                    # We can't save masked points properly, as we don't maintain
-                    # a fill_value.  (Load will not record one, either).
-                    msg = "Cell measures with missing data are not supported."
-                    raise ValueError(msg)
-
             if is_dimcoord:
                 # By definition of a CF-netCDF coordinate variable this
                 # coordinate must be 1-D and the name of the CF-netCDF variable

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

@@ -1051,38 +1051,5 @@ def test_geo_cs(self):
         self._test(coord_system, expected)
 
 
-class Test__create_cf_cell_measure_variable(tests.IrisTest):
-    # Saving of masked data is disallowed.
-
-    # Attribute is substituted in test_Saver__lazy.
-    array_lib = np
-
-    def setUp(self):
-        self.cube = stock.lat_lon_cube()
-        self.names_map = ["latitude", "longitude"]
-        masked_array = self.array_lib.ma.masked_array(
-            [0, 1, 2], mask=[True, False, True]
-        )
-        self.cm = iris.coords.CellMeasure(masked_array, var_name="cell_area")
-        self.cube.add_cell_measure(self.cm, data_dims=0)
-        self.exp_emsg = "Cell measures with missing data are not supported."
-
-    def test_masked_data__insitu(self):
-        # Test that the error is raised in the right place.
-        with self.temp_filename(".nc") as nc_path:
-            saver = Saver(nc_path, "NETCDF4")
-            with self.assertRaisesRegex(ValueError, self.exp_emsg):
-                saver._create_generic_cf_array_var(
-                    self.cube, self.names_map, self.cm
-                )
-
-    def test_masked_data__save_pipeline(self):
-        # Test that the right error is raised by the saver pipeline.
-        with self.temp_filename(".nc") as nc_path:
-            with Saver(nc_path, "NETCDF4") as saver:
-                with self.assertRaisesRegex(ValueError, self.exp_emsg):
-                    saver.write(self.cube)
-
-
 if __name__ == "__main__":
     tests.main()

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

@@ -82,12 +82,6 @@ class Test_check_attribute_compliance__exception_handling(
     pass
 
 
-class Test__create_cf_cell_measure_variable(
-    LazyMixin, test_Saver.Test__create_cf_cell_measure_variable
-):
-    pass
-
-
 class TestStreamed(tests.IrisTest):
     def setUp(self):
         self.cube = stock.simple_2d()