Handle exception in case of no tiles are extracted

src/histolab/tiler.py

@@ -644,8 +644,12 @@ def _scores(self, slide: Slide) -> List[Tuple[float, CoordinatePair]]:
             List of tuples containing the score and the extraction coordinates for each
             tile. Each tuple represents a tile.
         """
-        grid_tiles = self._grid_tiles_generator(slide)
+        if next(self._grid_tiles_generator(slide), None) is None:
+            raise RuntimeError(
+                "No tiles have been generated. This could happen if `check_tissue=True`"
+            )
 
+        grid_tiles = self._grid_tiles_generator(slide)
         scores = []
 
         for tile, tile_wsi_coords in grid_tiles:

tests/unit/test_tiler.py

@@ -745,21 +745,44 @@ def it_can_calculate_scores(self, request):
         _grid_tiles_generator = method_mock(
             request, ScoreTiler, "_grid_tiles_generator"
         )
-        _grid_tiles_generator.return_value = [(tile, coords), (tile, coords)]
+        # it needs to be a generator
+        _grid_tiles_generator.return_value = ((tile, coords) for i in range(3))
         _scorer = instance_mock(request, RandomScorer)
         _scorer.side_effect = [0.5, 0.7]
         score_tiler = ScoreTiler(_scorer, (10, 10), 2, 0)
 
         scores = score_tiler._scores(slide)
 
-        _grid_tiles_generator.assert_called_once_with(score_tiler, slide)
+        assert _grid_tiles_generator.call_args_list == [
+            call(score_tiler, slide),
+            call(score_tiler, slide),
+        ]
         assert _scorer.call_args_list == [call(tile), call(tile)]
         assert type(scores) == list
         assert type(scores[0]) == tuple
         assert type(scores[0][0]) == float
         assert type(scores[0][1]) == CoordinatePair
         assert scores == [(0.5, coords), (0.7, coords)]
 
+    def but_it_raises_runtimeerror_if_no_tiles_are_extracted(self, request):
+        slide = instance_mock(request, Slide)
+        _grid_tiles_generator = method_mock(
+            request, ScoreTiler, "_grid_tiles_generator"
+        )
+        # it needs to be an empty generator
+        _grid_tiles_generator.return_value = (n for n in [])
+        score_tiler = ScoreTiler(None, (10, 10), 2, 0)
+
+        with pytest.raises(RuntimeError) as err:
+            score_tiler._scores(slide)
+
+        _grid_tiles_generator.assert_called_once_with(score_tiler, slide)
+        assert isinstance(err.value, RuntimeError)
+        assert (
+            str(err.value)
+            == "No tiles have been generated. This could happen if `check_tissue=True`"
+        )
+
     def it_can_calculate_highest_score_tiles(
         self, request, highest_score_tiles_fixture
     ):