input: 
  def test_blockchain():
      """Test the basic blockchain system by creating a blockchain, adding a block, and retrieving the blockchain.
      >>> blockchain = Blockchain()
      >>> blockchain.add_block({'timestamp': '2023-10-01 12:34:56', 'data': 'First block data'})
      >>> blockchain.add_block({'timestamp': '2023-10-02 12:34:56', 'data': 'Second block data'})
      >>> blockchain.get_chain()
      '[
        {
          "index": 0,
          "timestamp": "2023-10-01 12:34:56",
          "data": "First block data",
          "previous_hash": null,
          "hash": "..."
        },
        {
          "index": 1,
          "timestamp": "2023-10-02 12:34:56",
          "data": "Second block data",
          "previous_hash": "...First block hash here...",
          "hash": "..."
        }
      ]'
      """
  
output:     
      blockchain = Blockchain()
      blockchain.add_block({'timestamp': '2023-10-01 12:34:56', 'data': 'First block data'})
      blockchain.add_block({'timestamp': '2023-10-02 12:34:56', 'data': 'Second block data'})
      assert blockchain.get_chain() == '[
        {
          "index": 0,
          "timestamp": "2023-10-01 12:34:56",
          "data": "First block data",
          "previous_hash": null,
          "hash": "..."
        },
        {
          "index": 1,
          "timestamp": "2023-10-02 12:34:56",
          "data": "Second block data",
          "previous_hash": "...First block hash here...",
          "hash": "..."
        }
      ]'
  