added corresponding test

src/data_handling/data_preparation.py

@@ -354,7 +354,6 @@ class DataPrep(object):
             intersect = reduce(np.intersect1d, (non_nan_history.coords[dim].values, non_nan_label.coords[dim].values, non_nan_observation.coords[dim].values))
 
         min_length = self.kwargs.get("min_length", 0)
-        length = len(intersect)
         if len(intersect) < max(min_length, 1):
             self.history = None
             self.label = None

test/test_data_handling/test_data_preparation.py

@@ -287,6 +287,14 @@ class TestDataPrep:
         assert remaining_len == data.label.datetime.shape
         assert remaining_len == data.observation.datetime.shape
 
+    def test_remove_nan_too_short(self, data):
+        data.kwargs["min_length"] = 4000  # actual length of series is 3940
+        data.make_history_window('variables', -12, 'datetime')
+        data.make_labels('variables', 'o3', 'datetime', 3)
+        data.make_observation('variables', 'o3', 'datetime')
+        data.remove_nan('datetime')
+        assert not any([data.history, data.label, data.observation])
+
     def test_create_index_array(self, data):
         index_array = data.create_index_array('window', range(1, 4))
         assert np.testing.assert_array_equal(index_array.data, [1, 2, 3]) is None