Fix custom-label delete test after topic remapping.

Deleting topic 0 still leaves a topic 0 because remaining topics are renumbered by frequency.

Author: gyanu2507

tests/test_reduction/test_delete.py

@@ -74,10 +74,12 @@ def test_delete_keeps_custom_labels(model, request):
 
     remaining = [topic for topic in sorted(set(topic_model.topics_)) if topic != -1]
     topic_to_delete = remaining[0]
+    before = len(set(topic_model.topics_))
 
     topic_model.delete_topics([topic_to_delete])
 
     unique_topics = sorted(set(topic_model.topics_))
     assert isinstance(topic_model.custom_labels_, list)
     assert len(topic_model.custom_labels_) == len(unique_topics)
-    assert topic_to_delete not in unique_topics
+    # Remaining topics are remapped by frequency, so the deleted id can reappear.
+    assert len(unique_topics) < before