code: def data():
      """A dataframe with quantitative and nominal columns"""
      return pd.DataFrame(
          {
              "x": range(10),
              "y": range(10),
              "z": range(10),
              "a": list("ABCABCABCA"),
              "b": list("ABCABCABCA"),
          }
      )
  
imports: import pytest
  import pandas
  import pdvega
  from .utils import validate_vegalite
label_desc: Use image node_id 1 for calling a global function with example usage: data() and returns: pd