code: def test_sep_default_parameter():
      """Test that the default parameter is a pipe character `|`."""
      df = pd.DataFrame(
          {
              "col1": ["A|B", "B|C|D", "E|F", "A|E|F"],
              "col2": [1, 2, 3, 4],
          }
      )
      result = df.expand_column("col1")
  
      assert result.shape[1] == 8
  
imports: import pandas
  import pytest
label_desc: Use image node_id 3 for calling a global function with example usage: test_sep_default_parameter() without return types