tests: Add a sha256sum_file function to util

Author: achow101

test/functional/test_framework/util.py

@@ -8,6 +8,7 @@
 from binascii import unhexlify
 from decimal import Decimal, ROUND_DOWN
 from subprocess import CalledProcessError
+import hashlib
 import inspect
 import json
 import logging
@@ -260,6 +261,14 @@ def wait_until_helper(predicate, *, attempts=float('inf'), timeout=float('inf'),
         raise AssertionError("Predicate {} not true after {} seconds".format(predicate_source, timeout))
     raise RuntimeError('Unreachable')
 
+def sha256sum_file(filename):
+    h = hashlib.sha256()
+    with open(filename, 'rb') as f:
+        d = f.read(4096)
+        while len(d) > 0:
+            h.update(d)
+            d = f.read(4096)
+    return h.digest()
 
 # RPC/P2P connection constants and functions
 ############################################