code: def test_opacity_single(self):
      options = self._add_default_options(
          fill_opacity=0.2, stroke_opacity=0.5
      )
      symbols = symbol_layer(self.locations, **options)
      for symbol in symbols.markers:
          assert symbol.fill_opacity == 0.2
          assert symbol.stroke_opacity == 0.5
  
imports: import unittest
  import pytest
  import numpy
  import traitlets
  from ..marker import MarkerOptions, Marker, Markers, Symbol, marker_layer, symbol_layer
label_desc: Use image node_id 15 for calling the SymbolLayer obj's underlying member method code with example usage: obj.test_opacity_single() without return types