code: def test_colorscale_symmetric_cmap(vmin, vmax):
      """Test colorscale with symmetric cmap and positive values."""
      colors = colorscale("jet", np.arange(15), vmin=vmin, vmax=vmax)
      assert (colors["vmin"], colors["vmax"]) == (-7, 7)
      assert colors["cmap"].N == 256
      assert (colors["norm"].vmax, colors["norm"].vmin) == (7, -7)
      assert colors["symmetric_cmap"]
  
imports: import base64
  import os
  import re
  import tempfile
  import numpy
  import pytest
  from nilearn.datasets import fetch_surf_fsaverage
  from nilearn.plotting.js_plotting_utils import add_js_lib, colorscale, decode, encode, get_html_template, mesh_to_plotly, to_color_strings
  from nilearn.surface import load_surf_mesh
label_desc: Use image node_id 7 for calling a global function with example usage: test_colorscale_symmetric_cmap(vmin, vmax) without return types