add tests for handling of empty pandas objects in constructors (#2735)

* add tests for GH#697 - handling of empty pandas objects in constructors

* make pep8 happy

Author: Joe Hamman

xarray/tests/test_dataarray.py

@@ -2872,6 +2872,15 @@ def test_to_and_from_series(self):
             expected_da,
             DataArray.from_series(actual).drop(['x', 'y']))
 
+    def test_to_and_from_empty_series(self):
+        # GH697
+        expected = pd.Series([])
+        da = DataArray.from_series(expected)
+        assert len(da) == 0
+        actual = da.to_series()
+        assert len(actual) == 0
+        assert expected.equals(actual)
+
     def test_series_categorical_index(self):
         # regression test for GH700
         if not hasattr(pd, 'CategoricalIndex'):

xarray/tests/test_dataset.py

@@ -2980,6 +2980,15 @@ def test_to_and_from_dataframe(self):
         expected = pd.DataFrame([[]], index=idx)
         assert expected.equals(actual), (expected, actual)
 
+    def test_to_and_from_empty_dataframe(self):
+        # GH697
+        expected = pd.DataFrame({'foo': []})
+        ds = Dataset.from_dataframe(expected)
+        assert len(ds['foo']) == 0
+        actual = ds.to_dataframe()
+        assert len(actual) == 0
+        assert expected.equals(actual)
+
     def test_from_dataframe_non_unique_columns(self):
         # regression test for GH449
         df = pd.DataFrame(np.zeros((2, 2)))