fix tests from modified get_element_instances (#287)

Author: LucaMarconato

tests/_images/Labels_label_categorical_color.png

@@ -5,8 +5,9 @@
 import pandas as pd
 import pytest
 import scanpy as sc
+from anndata import AnnData
 from spatial_image import to_spatial_image
-from spatialdata import SpatialData, deepcopy
+from spatialdata import SpatialData, deepcopy, get_element_instances
 from spatialdata.models import TableModel
 
 import spatialdata_plot  # noqa: F401
@@ -208,3 +209,27 @@ def test_plot_subset_categorical_label_maintains_order_when_palette_overwrite(se
         sdata_blobs.pl.render_labels(
             "blobs_labels", color="which_max", groups=["channel_0_sum"], palette="red"
         ).pl.show(ax=axs[1])
+
+    def test_plot_label_categorical_color(self, sdata_blobs: SpatialData):
+        self._make_tablemodel_with_categorical_labels(sdata_blobs, labels_name="blobs_labels")
+        sdata_blobs.pl.render_labels("blobs_labels", color="category").pl.show()
+
+    def _make_tablemodel_with_categorical_labels(self, sdata_blobs, labels_name: str):
+        instances = get_element_instances(sdata_blobs[labels_name])
+        n_obs = len(instances)
+        adata = AnnData(
+            RNG.normal(size=(n_obs, 10)),
+            obs=pd.DataFrame(RNG.normal(size=(n_obs, 3)), columns=["a", "b", "c"]),
+        )
+        adata.obs["instance_id"] = instances.values
+        adata.obs["category"] = RNG.choice(["a", "b", "c"], size=adata.n_obs)
+        adata.obs["category"][:3] = ["a", "b", "c"]
+        adata.obs["region"] = labels_name
+        table = TableModel.parse(
+            adata=adata,
+            region_key="region",
+            instance_key="instance_id",
+            region=labels_name,
+        )
+        sdata_blobs["other_table"] = table
+        sdata_blobs["other_table"].obs["category"] = sdata_blobs["other_table"].obs["category"].astype("category")