code: def test_df_area_unstacked():
      df = pd.DataFrame({"x": [1, 4, 2, 3, 5], "y": [6, 3, 4, 5, 2]})
  
      plot = df.vgplot.area(stacked=False)
      utils.validate_vegalite(plot)
      assert plot.mark == "area"
      utils.check_encodings(
          plot,
          x="index",
          y="value",
          color="variable",
          opacity=utils.IGNORE,
      )
      data = plot.data
      assert set(pd.unique(data["variable"])) == {"x", "y"}
      assert plot["encoding"]["y"]["stack"] is None
      assert plot["encoding"]["opacity"]["value"] == 0.7
  
imports: import pytest
  import pandas
  import altair
  from pdvega.tests import utils
label_desc: Use image node_id 18 for calling a global function with example usage: test_df_area_unstacked() without return types