Add Pixel.northeast/southwest properties

- the properties are needed for the drawing functionalitites

tests/db/test_grids.py

@@ -205,7 +205,7 @@ class TestGridification:
     @pytest.mark.db
     @pytest.mark.no_cover
     @pytest.mark.parametrize('side_length', [250, 500, 1_000, 2_000, 4_000, 8_000])
-    def test_make_random_grids(  # noqa:WPS211
+    def test_make_random_grids(  # noqa:WPS211,WPS218
         self, db_session, city, make_address, make_restaurant, make_order, side_length,
     ):
         """With 100 random `Address` objects, a grid must have ...
@@ -228,5 +228,12 @@ class TestGridification:
         assert isinstance(result, db.Grid)
         assert 1 <= len(result.pixels) <= n_pixels_x * n_pixels_y
 
+        # Sanity checks for `Pixel.southwest` and `Pixel.northeast`.
+        for pixel in result.pixels:
+            assert abs(pixel.southwest.x - pixel.n_x * side_length) < 2
+            assert abs(pixel.southwest.y - pixel.n_y * side_length) < 2
+            assert abs(pixel.northeast.x - (pixel.n_x + 1) * side_length) < 2
+            assert abs(pixel.northeast.y - (pixel.n_y + 1) * side_length) < 2
+
         db_session.add(result)
         db_session.commit()

tests/db/test_pixels.py

@@ -87,3 +87,31 @@ class TestProperties:
         result = pixel.area
 
         assert result == 1.0
+
+    def test_northeast(self, pixel, city):
+        """Test `Pixel.northeast` property."""
+        result = pixel.northeast
+
+        assert abs(result.x - pixel.side_length) < 2
+        assert abs(result.y - pixel.side_length) < 2
+
+    def test_northeast_is_cached(self, pixel):
+        """Test `Pixel.northeast` property."""
+        result1 = pixel.northeast
+        result2 = pixel.northeast
+
+        assert result1 is result2
+
+    def test_southwest(self, pixel, city):
+        """Test `Pixel.southwest` property."""
+        result = pixel.southwest
+
+        assert abs(result.x) < 2
+        assert abs(result.y) < 2
+
+    def test_southwest_is_cached(self, pixel):
+        """Test `Pixel.southwest` property."""
+        result1 = pixel.southwest
+        result2 = pixel.southwest
+
+        assert result1 is result2

tests/db/utils/test_locations.py

@@ -140,6 +140,13 @@ class TestProperties:
 
         assert result == ZONE
 
+    def test_zone_details(self, location):
+        """Test `Location.zone_details` property."""
+        result = location.zone_details
+
+        zone, band = result
+        assert ZONE == f'{zone}{band}'
+
 
 class TestRelateTo:
     """Test the `Location.relate_to()` method and the `.x` and `.y` properties."""