code: def test_construct_from_dict_with_alpha(self):
      rgb = RGB(
          {
              "x": [1, 2, 3],
              "y": [1, 2, 3],
              ("R", "G", "B", "A"): self.rgb_array,
          }
      )
      self.assertEqual(len(rgb.vdims), 4)
  
imports: import numpy
  from holoviews.element import HSV, RGB, Curve, Image, QuadMesh, Raster
  from holoviews.element.comparison import ComparisonTestCase
label_desc: Use image node_id 4 for calling the TestRGB obj's underlying member method code with example usage: obj.test_construct_from_dict_with_alpha() without return types