docstr: Assert all elements outside the blocks are zero.
code: def _validate_sizes(self, block_diag_tensor, sizes):
      """Assert all elements outside the blocks are zero."""
      data = [np.ones(shape=s) for s in sizes]
      mask = 1.0 - linalg.block_diag(*data)
  
      self.assertAllEqual(
          tf.sparse.to_dense(block_diag_tensor) * mask,
          np.zeros_like(mask),
      )
  
imports: from absl.testing import parameterized
  import numpy
  from scipy import linalg
  import tensorflow
  from tensorflow_graphics.geometry.convolution import utils
  from tensorflow_graphics.util import test_case
label_desc: Use image node_id 1 for calling the UtilsConvertToBlockDiag2dTests obj's underlying member method code with example usage: obj._validate_sizes(block_diag_tensor, sizes) without return types