text: from ipyvolume import TransferFunction
  from nwbwidgets.utils.cmaps import (
      linear_transfer_function,
      matplotlib_transfer_function,
  )
  
  
  def test_linear_transfer_function():
      assert isinstance(
          linear_transfer_function("blue", reverse_opacity=True), TransferFunction
      )
  
  
  def test_matplotlib_transfer_function():
      assert isinstance(matplotlib_transfer_function("PuBuGn_r"), TransferFunction)
  