Properly assert ESMF enums in test suite

Enums should be compared by identity, not value.
Ref: https://docs.python.org/3/library/enum.html#comparisons

xesmf/tests/test_backend.py

@@ -41,25 +41,6 @@
 data4D_in = ds_in['data4D'].values
 
 
-def test_flag():
-    # some shortcuts for ESMF flags
-    assert ESMF.StaggerLoc.CENTER == 0
-    assert ESMF.StaggerLoc.CORNER == 3
-
-    assert ESMF.CoordSys.CART == 0
-    assert ESMF.CoordSys.SPH_DEG == 1  # only use this!
-    assert ESMF.CoordSys.SPH_RAD == 2
-
-    assert ESMF.UnmappedAction.ERROR == 0
-    assert ESMF.UnmappedAction.IGNORE == 1  # only use this!
-
-    assert ESMF.RegridMethod.BILINEAR == 0
-    assert ESMF.RegridMethod.PATCH == 1
-    assert ESMF.RegridMethod.CONSERVE == 2
-    assert ESMF.RegridMethod.NEAREST_STOD == 3
-    assert ESMF.RegridMethod.NEAREST_DTOS == 4
-
-
 def test_warn_f_on_array():
     a = np.zeros([2, 2], order='C')
     with pytest.warns(UserWarning):
@@ -94,7 +75,7 @@ def test_esmf_grid_with_corner():
     # make sure meta data agree
     assert not grid.has_corners  # no corner yet!
     assert grid.staggerloc == [True, False, False, False]
-    assert grid.coord_sys == 1
+    assert grid.coord_sys is ESMF.CoordSys.SPH_DEG
     assert grid.rank == 2
     assert_equal(grid.size[0], lon.T.shape)
     assert_equal(grid.upper_bounds[0], lon.T.shape)
@@ -121,8 +102,8 @@ def test_esmf_build_bilinear():
     grid_out = esmf_grid(lon_out.T, lat_out.T)
 
     regrid = esmf_regrid_build(grid_in, grid_out, 'bilinear')
-    assert regrid.unmapped_action == 1
-    assert regrid.regrid_method == 0
+    assert regrid.unmapped_action is ESMF.UnmappedAction.IGNORE
+    assert regrid.regrid_method is ESMF.RegridMethod.BILINEAR
 
     # they should share the same memory
     regrid.srcfield.grid is grid_in
@@ -156,7 +137,7 @@ def test_regrid():
         os.remove(filename)
     regrid = esmf_regrid_build(grid_in, grid_out, 'conservative',
                                filename=filename)
-    assert regrid.regrid_method == 2
+    assert regrid.regrid_method is ESMF.RegridMethod.CONSERVE
 
     # apply regridding using ESMPy's native method
     data_out_esmpy = esmf_regrid_apply(regrid, data_in.T).T