code: def test_cannot_re_add_relationships_that_already_exists(es):
      before_len = len(es.relationships)
      es.add_relationship(relationship=es.relationships[0])
      after_len = len(es.relationships)
      assert before_len == after_len
  
imports: import pandas
  import pytest
  from featuretools import EntitySet
  from featuretools.tests.testing_utils import backward_path, forward_path
label_desc: Use image node_id 1 for calling a global function with example usage: test_cannot_re_add_relationships_that_already_exists(es) without return types