test: Add multidict to support dictionary with duplicate key (laanwj)

test/functional/rawtransactions.py

@@ -15,6 +15,25 @@ Test the following RPCs:
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
 
+
+class multidict(dict):
+    """Dictionary that allows duplicate keys.
+
+    Constructed with a list of (key, value) tuples. When dumped by the json module,
+    will output invalid json with repeated keys, eg:
+    >>> json.dumps(multidict([(1,2),(1,2)])
+    '{"1": 2, "1": 2}'
+
+    Used to test calls to rpc methods with repeated keys in the json object."""
+
+    def __init__(self, x):
+        dict.__init__(self, x)
+        self.x = x
+
+    def items(self):
+        return self.x
+
+
 # Create one-input, one-output, no-fee transaction:
 class RawTransactionsTest(BitcoinTestFramework):
     def set_test_params(self):