code: def test_relation_tags():
      # set 3 labels for 2 spans (HU is tagged twice with different tags)
      sentence = Sentence(
          "Humboldt Universität zu Berlin is located in Berlin ."
      )
  
      # create two relation label
      Relation(sentence[0:4], sentence[7:8]).add_label(
          "rel", "located in"
      )
      Relation(sentence[0:2], sentence[3:4]).add_label(
          "rel", "university of"
      )
      Relation(sentence[0:2], sentence[3:4]).add_label(
          "syntactic", "apposition"
      )
  
      # there should be two relation labels
      labels: List[Label] = sentence.get_labels("rel")
      assert len(labels) == 2
      assert labels[0].value == "located in"
      assert labels[1].value == "university of"
  
      # there should be one syntactic labels
      labels: List[Label] = sentence.get_labels("syntactic")
      assert len(labels) == 1
  
      # there should be two relations, one with two and one with one label
      relations: List[Relation] = sentence.get_relations("rel")
      assert len(relations) == 2
      assert len(relations[0].labels) == 1
      assert len(relations[1].labels) == 2
  
file_path: flair/tests/test_labels.py
imports: from typing import List
  from flair.data import Label, Relation, Sentence, Span
label_desc: Use image node_id 4 for calling a global function with example usage: test_relation_tags() without return types