Added compute hash doctest

Author: LetitiaGilbert

blockchain/simple_blockchain.py

@@ -45,12 +45,19 @@ def compute_hash(self, nonce: int) -> str:
 
         Returns:
             str: Hexadecimal hash string.
+
+        >>> block = Block(0, "Genesis", "0", difficulty=2)
+        >>> len(block.compute_hash(0)) == 64
+        True
+        >>> isinstance(block.compute_hash(0), str)
+        True
         """
         block_string = (
             f"{self.index}{self.timestamp}{self.data}{self.previous_hash}{nonce}"
         )
         return hashlib.sha256(block_string.encode()).hexdigest()
 
+
     def mine_block(self, difficulty: int) -> Tuple[int, str]:
         """
         Simple Proof-of-Work mining algorithm.