code: def test_overlay_xlabel(self):
      overlay = (Curve(range(10)) * Curve(range(10))).opts(
          xlabel="custom x-label"
      )
      axes = mpl_renderer.get_plot(overlay).handles["axis"]
      self.assertEqual(axes.get_xlabel(), "custom x-label")
  
imports: import numpy
  from holoviews.core import DynamicMap, HoloMap, NdOverlay, Overlay
  from holoviews.element import Curve, Scatter
  from ...utils import LoggingComparisonTestCase
  from .test_plot import TestMPLPlot, mpl_renderer
label_desc: Use image node_id 9 for calling the TestOverlayPlot obj's underlying member method code with example usage: obj.test_overlay_xlabel() without return types