Test and fix RegionSelector doctest fail

gwcs/selector.py

@@ -531,7 +531,20 @@ def __init__(self, inputs, outputs, selector, label_mapper, undefined_transform_
             raise ValueError('"0" and " " are not allowed as keys.')
         self._input_units_strict = {key: False for key in self._inputs}
         self._input_units_allow_dimensionless = {key: False for key in self._inputs}
-        super(RegionsSelector, self).__init__(n_models=1, name=name, **kwargs)
+        super().__init__(n_models=1, name=name, **kwargs)
+        # Validate uses_quantity at init time for nicer error message
+        self.uses_quantity  # noqa
+
+    @property
+    def uses_quantity(self):
+        all_uses_quantity = [t.uses_quantity for t in self._selector.values()]
+        not_all_uses_quantity = [not uq for uq in all_uses_quantity]
+        if all(all_uses_quantity):
+            return True
+        elif not_all_uses_quantity:
+            return False
+        else:
+            raise ValueError("You can not mix models which use quantity and do not use quantity inside a RegionSelector")
 
     def set_input(self, rid):
         """

gwcs/tests/test_region.py

@@ -8,8 +8,9 @@
 from numpy.testing import assert_equal, assert_allclose
 from astropy.modeling import models
 import pytest
-from .. import region, selector
-from .. import utils as gwutils
+from gwcs import region, selector, WCS
+from gwcs import utils as gwutils
+from gwcs import coordinate_frames as cf
 
 
 def test_LabelMapperArray_from_vertices_int():
@@ -237,6 +238,10 @@ def test_RegionsSelector():
     reg_selector.undefined_transform_value = -100
     assert_equal(reg_selector(0, 0), [-100, -100])
 
+    wcs = WCS(forward_transform=reg_selector, output_frame=cf.Frame2D())
+    out = wcs(1, 1)
+    assert out == (-100, -100)
+
 
 def test_overalpping_ranges():
     """