rewrote the subset selector for sgrid, added test based on example notebook

tests/test_grids/test_sgrid.py

@@ -6,6 +6,14 @@
 import xarray_subset_grid.accessor  # noqa: F401
 from xarray_subset_grid.utils import ray_tracing_numpy
 # open dataset as zarr object using fsspec reference file system and xarray
+
+from xarray_subset_grid.utils import get_test_file_dir
+
+from gridded import Variable, VectorVariable
+
+test_dir = get_test_file_dir()
+sample_sgrid_file = os.path.join(test_dir, 'arakawa_c_test_grid.nc')
+
 def test_polygon_subset():
     '''
     This is a basic integration test for the subsetting of a ROMS sgrid dataset using a polygon.
@@ -51,4 +59,18 @@ def test_polygon_subset():
     #Note that this needs to be better generalized; it's not trivial to write a test that works in all potential cases.
     assert ds_subset['lon_rho'][0,0] < ds_subset['lon_psi'][0,0] and ds_subset['lon_rho'][0,1] > ds_subset['lon_psi'][0,0]
 
-    #ds_subset.temp_sur.isel(ocean_time=0).plot(x="lon_rho", y="lat_rho")
+    #ds_subset.temp_sur.isel(ocean_time=0).plot(x="lon_rho", y="lat_rho")
+
+def test_polygon_subset_2(): 
+    ds = xr.open_dataset(sample_sgrid_file)
+    polygon = np.array(
+        [6.5, 37.5],
+        [6.5, 39.5],
+        [9.5, 40.5],
+        [8.5, 37.5],
+        [6.5, 37.5]
+    )
+    ds_subset = ds.xsg.subset_polygon(polygon)
+
+    breakpoint()
+

tests/utilities.py

@@ -0,0 +1,24 @@
+"""
+Assorted utilities useful for the tests.
+"""
+
+import os
+import contextlib
+
+try:
+    import urllib.request as urllib_request  # for python 3
+except ImportError:
+    import urllib2 as urllib_request  # for python 2
+
+import pytest
+import glob
+
+from .get_remote_data import get_datafile
+
+
+def get_test_file_dir():
+    """
+    returns the test file dir path
+    """
+    test_file_dir = os.path.join(os.path.dirname(__file__), 'test_data')
+    return test_file_dir