code: def test_imshow_backend(backend):
      fig = px.imshow(img_rgb, binary_backend=backend)
      decoded_img = decode_image_string(fig.data[0].source)
      assert np.all(decoded_img == img_rgb)
  
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 21 for calling a global function with example usage: test_imshow_backend(backend) without return types