code: def test_colorscale():
      fig = px.imshow(img_gray)
      plasma_first_color = px.colors.sequential.Plasma[0]
      assert fig.layout.coloraxis1.colorscale[0] == (
          0.0,
          plasma_first_color,
      )
      fig = px.imshow(img_gray, color_continuous_scale="Viridis")
      assert fig.layout.coloraxis1.colorscale[0] == (0.0, "#440154")
  
imports: import plotly.express
  import numpy
  import pytest
  import xarray
  from PIL import Image
  from io import BytesIO
  import base64
  import datetime
  from plotly.express.imshow_utils import rescale_intensity
label_desc: Use image node_id 6 for calling a global function with example usage: test_colorscale() without return types