code: def test_equal_clims(texture_format):
      """Test that equal clims produce a min cmap value."""
      size = (40, 40)
      np.random.seed(0)  # make tests the same every time
      data = _make_test_data(size[:1] * 3, np.float32)
      with TestingCanvas(size=size, bgcolor="k") as c:
          v = c.central_widget.add_view(border_width=0)
          scene.visuals.Volume(
              data,
              interpolation="nearest",
              clim=(128.0, 128.0),  # equal clims
              cmap="viridis",  # something with a non-black min value
              parent=v.scene,
              method="mip",
              texture_format=texture_format,
          )
          v.camera = "arcball"
          v.camera.fov = 0
          v.camera.scale_factor = 40.0
          v.camera.center = (19.5, 19.5, 19.5)
  
          rendered = c.render()[..., :3]
          # not all black
          assert rendered.sum() != 0
          # not all white
          assert rendered.sum() != 255 * rendered.size
          # should be all the same value
          r_unique = np.unique(rendered[..., 0])
          g_unique = np.unique(rendered[..., 1])
          b_unique = np.unique(rendered[..., 2])
          assert r_unique.size == 1
          assert g_unique.size == 1
          assert b_unique.size == 1
  
imports: import pytest
  import numpy
  from vispy import scene
  from vispy.testing import TestingCanvas, requires_application, run_tests_if_main, requires_pyopengl, raises
  from vispy.testing.image_tester import assert_image_approved, downsample
  from vispy.testing.rendered_array_tester import compare_render, max_for_dtype
label_desc: Use image node_id 6 for calling a global function with example usage: test_equal_clims(texture_format) without return types