docstr: Test for exception with negative weights.
docstr_tok: ["Test","for","exception","with","negative","weights","."]
code: def test_weighted_sampler_negative_weights(self):
      """Test for exception with negative weights."""
      vertices, faces = mesh_test_utils.create_square_triangle_mesh()
      face_wts = np.array([-0.3, 0.1, 0.5, 0.6], dtype=np.float32)
      num_samples = 10
      error_msg = "Condition x >= y did not hold."
      with self.assertRaisesRegexp(
          tf.errors.InvalidArgumentError, error_msg
      ):
          sampler.weighted_random_sample_triangle_mesh(
              vertices, faces, num_samples, face_weights=face_wts
          )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from absl.testing import parameterized
  import numpy
  from six.moves import range
  import tensorflow
  from tensorflow_graphics.geometry.representation.mesh import sampler
  from tensorflow_graphics.geometry.representation.mesh.tests import mesh_test_utils
  from tensorflow_graphics.util import test_case
label_desc: Use image node_id 12 for calling the MeshSamplerTest obj's underlying member method code with example usage: obj.test_weighted_sampler_negative_weights() without return types