code: def test_set_background():
      out = tf.set_background(img1)
      assert out.equals(img1)
      sol = tf.Image(
          np.array(
              [[0xFF00FFFF, 0xFF0000FF], [0xFF0000FF, 0xFF00FF7D]],
              dtype="uint32",
          ),
          coords=coords2,
          dims=dims,
      )
      out = tf.set_background(img1, "red")
      assert out.equals(sol)
  
imports: from __future__ import annotations
  from io import BytesIO
  import numpy
  import xarray
  import dask.array
  import PIL
  import pytest
  import datashader.transfer_functions
  from datashader.tests.test_pandas import assert_eq_ndarray, assert_eq_xr, assert_image_close
label_desc: Use image node_id 19 for calling a global function with example usage: test_set_background() without return types