code: def test_unpack_batch_mapping():
      batch = [{"a": [1, 2], "b": 1}, {"a": [3], "b": 2}]
      assert MappingPackerUnpacker.unpack_batch(batch, {}, {}) == {
          "a": [[1, 2], [3]],
          "b": [1, 2],
      }
  
imports: from fastNLP.core.collators.packer_unpacker import MappingPackerUnpacker, NestedMappingPackerUnpacker, SequencePackerUnpacker
label_desc: Use image node_id 1 for calling a global function with example usage: test_unpack_batch_mapping() without return types