code: def test_sparse_to_dense_mask_string(self):
      op = core.CreateOperator(
          "SparseToDenseMask",
          ["indices", "values", "default", "lengths"],
          ["output"],
          mask=[999999999, 2, 6],
      )
      workspace.FeedBlob(
          "indices",
          np.array([2, 4, 6, 1, 2, 999999999, 2], dtype=np.int32),
      )
      workspace.FeedBlob(
          "values",
          np.array(["1", "2", "3", "4", "5", "6", "7"], dtype="S"),
      )
      workspace.FeedBlob("default", np.array("-1", dtype="S"))
      workspace.FeedBlob("lengths", np.array([3, 4], dtype=np.int32))
      workspace.RunOperatorOnce(op)
      output = workspace.FetchBlob("output")
      expected = np.array(
          [["-1", "1", "3"], ["6", "7", "-1"]], dtype="S"
      )
      self.assertEqual(output.shape, expected.shape)
      np.testing.assert_array_equal(output, expected)
  
file_path: pytorch/caffe2/python/sparse_to_dense_mask_test.py
imports: from caffe2.python import core, workspace
  from caffe2.python.test_util import TestCase
  import numpy
label_desc: Use image node_id 4 for calling the TestSparseToDenseMask obj's underlying member method code with example usage: obj.test_sparse_to_dense_mask_string() without return types