code: def test_alpha_dim_overlay(self, df, kind, backend):
      plot = df.hvplot(
          "x", "y", alpha="number", by="category", kind=kind
      )
      opts = Store.lookup_options(backend, plot.last, "style")
      assert opts.kwargs["alpha"] == "number"
      assert "number" in plot.last.vdims
  
imports: import hvplot
  import holoviews
  import numpy
  import pandas
  import pytest
  import xarray
  from holoviews import Store
  from holoviews.core.options import Options, OptionTree
label_desc: Use image node_id 10 for calling the TestOptions obj's underlying member method code with example usage: obj.test_alpha_dim_overlay(df, kind, backend) without return types