code: def test_add(self):
      ri1 = splits.ReadInstruction.from_spec("train[10:20]")
      ri2 = splits.ReadInstruction.from_spec("test[10:20]")
      ri3 = splits.ReadInstruction.from_spec("train[1:5]")
      ri = ri1 + ri2 + ri3
      self.assertEqual(
          str(ri),
          (
              "ReadInstruction('train[10:20]')"
              "+ReadInstruction('test[10:20]')"
              "+ReadInstruction('train[1:5]')"
          ),
      )
  
imports: from tensorflow_datasets import testing
  from tensorflow_datasets.core import naming
  from tensorflow_datasets.core import proto
  from tensorflow_datasets.core import splits
  from tensorflow_datasets.core.utils import shard_utils
  import tensorflow_datasets.public_api
label_desc: Use image node_id 6 for calling the ReadInstructionTest obj's underlying member method code with example usage: obj.test_add() without return types