extract/rename helper functions from rpc_packages.py

MOVEONLY; no change in behavior. Rename because there is another helper
funciton in chain_transaction in test_framework.util.py

test/functional/test_framework/wallet.py

@@ -16,6 +16,7 @@ from test_framework.messages import (
     CTxIn,
     CTxInWitness,
     CTxOut,
+    tx_from_hex,
 )
 from test_framework.script import (
     CScript,
@@ -176,3 +177,55 @@ class MiniWallet:
     def sendrawtransaction(self, *, from_node, tx_hex):
         from_node.sendrawtransaction(tx_hex)
         self.scan_tx(from_node.decoderawtransaction(tx_hex))
+
+def make_chain(node, address, privkeys, parent_txid, parent_value, n=0, parent_locking_script=None):
+    """Build a transaction that spends parent_txid.vout[n] and produces one output with
+    amount = parent_value with a fee deducted.
+    Return tuple (CTransaction object, raw hex, nValue, scriptPubKey of the output created).
+    """
+    inputs = [{"txid": parent_txid, "vout": n}]
+    my_value = parent_value - Decimal("0.0001")
+    outputs = {address : my_value}
+    rawtx = node.createrawtransaction(inputs, outputs)
+    prevtxs = [{
+        "txid": parent_txid,
+        "vout": n,
+        "scriptPubKey": parent_locking_script,
+        "amount": parent_value,
+    }] if parent_locking_script else None
+    signedtx = node.signrawtransactionwithkey(hexstring=rawtx, privkeys=privkeys, prevtxs=prevtxs)
+    assert signedtx["complete"]
+    tx = tx_from_hex(signedtx["hex"])
+    return (tx, signedtx["hex"], my_value, tx.vout[0].scriptPubKey.hex())
+
+def create_child_with_parents(node, address, privkeys, parents_tx, values, locking_scripts):
+    """Creates a transaction that spends the first output of each parent in parents_tx."""
+    num_parents = len(parents_tx)
+    total_value = sum(values)
+    inputs = [{"txid": tx.rehash(), "vout": 0} for tx in parents_tx]
+    outputs = {address : total_value - num_parents * Decimal("0.0001")}
+    rawtx_child = node.createrawtransaction(inputs, outputs)
+    prevtxs = []
+    for i in range(num_parents):
+        prevtxs.append({"txid": parents_tx[i].rehash(), "vout": 0, "scriptPubKey": locking_scripts[i], "amount": values[i]})
+    signedtx_child = node.signrawtransactionwithkey(hexstring=rawtx_child, privkeys=privkeys, prevtxs=prevtxs)
+    assert signedtx_child["complete"]
+    return signedtx_child["hex"]
+
+def create_raw_chain(node, first_coin, address, privkeys, chain_length=25):
+    """Helper function: create a "chain" of chain_length transactions. The nth transaction in the
+    chain is a child of the n-1th transaction and parent of the n+1th transaction.
+    """
+    parent_locking_script = None
+    txid = first_coin["txid"]
+    chain_hex = []
+    chain_txns = []
+    value = first_coin["amount"]
+
+    for _ in range(chain_length):
+        (tx, txhex, value, parent_locking_script) = make_chain(node, address, privkeys, txid, value, 0, parent_locking_script)
+        txid = tx.rehash()
+        chain_hex.append(txhex)
+        chain_txns.append(tx)
+
+    return (chain_hex, chain_txns)