new_contents: import Bio.Phylo
  from io import StringIO
  from pathlib import Path
  import pytest
  import sys
  
  # we assume (and assert) that this script is running from the tests/ directory
  sys.path.append(str(Path(__file__).parent.parent.parent))
  
  from augur.export_v2 import convert_tree_to_json_structure
  from augur.validate import ValidateError
  from augur.validate_export import ensure_no_duplicate_names
  
  
  class TestValidateExport():
      def test_export_without_duplicate_names(self):
          # Create a tree with unique tip names.
          tree = Bio.Phylo.read(StringIO("root(A, internal(B, C))"), "newick")
          metadata = {"A": {}, "B": {}, "C": {}, "root": {}, "internal": {}}
          root = convert_tree_to_json_structure(tree.root, metadata)
          ensure_no_duplicate_names(root, ValidateError)
  
      def test_export_with_duplicate_names(self):
          # Create a tree with duplicate tip names.
          tree = Bio.Phylo.read(StringIO("root(A, internal(B, B))"), "newick")
          metadata = {"A": {}, "B": {}, "root": {}, "internal": {}}
          root = convert_tree_to_json_structure(tree.root, metadata)
  
          with pytest.raises(ValidateError):
              ensure_no_duplicate_names(root, ValidateError)
  
subject: Add unit tests for ensure_no_duplicate_names