test: use MiniWallet to simplify mempool_package_limits.py tests

Moved `bulk_transaction` into MiniWallet class as `_bulk_tx` private
helper method to be used when the newly added `target_weight` option is
passed to `create_self_transfer*`

test/functional/test_framework/wallet.py

@@ -7,7 +7,6 @@
 from copy import deepcopy
 from decimal import Decimal
 from enum import Enum
-from random import choice
 from typing import (
     Any,
     List,
@@ -104,6 +103,16 @@ class MiniWallet:
     def _create_utxo(self, *, txid, vout, value, height):
         return {"txid": txid, "vout": vout, "value": value, "height": height}
 
+    def _bulk_tx(self, tx, target_weight):
+        """Pad a transaction with extra outputs until it reaches a target weight (or higher).
+        returns the tx
+        """
+        assert_greater_than_or_equal(target_weight, tx.get_weight())
+        while tx.get_weight() < target_weight:
+            script_pubkey = ( b"6a4d0200"  # OP_RETURN OP_PUSH2 512 bytes
+                + b"01" * 512 )
+            tx.vout.append(CTxOut(0, script_pubkey))
+
     def get_balance(self):
         return sum(u['value'] for u in self._utxos)
 
@@ -235,6 +244,7 @@ class MiniWallet:
         amount_per_output=0,
         sequence=0,
         fee_per_output=1000,
+        target_weight=0
     ):
         """
         Create and return a transaction that spends the given UTXOs and creates a
@@ -265,6 +275,10 @@ class MiniWallet:
         outputs_value_total = inputs_value_total - fee_per_output * num_outputs
         for o in tx.vout:
             o.nValue = amount_per_output or (outputs_value_total // num_outputs)
+
+        if target_weight:
+            self._bulk_tx(tx, target_weight)
+
         txid = tx.rehash()
         return {
             "new_utxos": [self._create_utxo(
@@ -278,7 +292,7 @@ class MiniWallet:
             "tx": tx,
         }
 
-    def create_self_transfer(self, *, fee_rate=Decimal("0.003"), fee=Decimal("0"), utxo_to_spend=None, locktime=0, sequence=0):
+    def create_self_transfer(self, *, fee_rate=Decimal("0.003"), fee=Decimal("0"), utxo_to_spend=None, locktime=0, sequence=0, target_weight=0):
         """Create and return a tx with the specified fee. If fee is 0, use fee_rate, where the resulting fee may be exact or at most one satoshi higher than needed."""
         utxo_to_spend = utxo_to_spend or self.get_utxo()
         assert fee_rate >= 0
@@ -305,9 +319,13 @@ class MiniWallet:
             tx.wit.vtxinwit[0].scriptWitness.stack = [CScript([OP_TRUE]), bytes([LEAF_VERSION_TAPSCRIPT]) + self._internal_key]
         else:
             assert False
-        tx_hex = tx.serialize().hex()
 
         assert_equal(tx.get_vsize(), vsize)
+
+        if target_weight:
+            self._bulk_tx(tx, target_weight)
+
+        tx_hex = tx.serialize().hex()
         new_utxo = self._create_utxo(txid=tx.rehash(), vout=0, value=send_value, height=0)
 
         return {"txid": new_utxo["txid"], "wtxid": tx.getwtxid(), "hex": tx_hex, "tx": tx, "new_utxo": new_utxo}
@@ -317,7 +335,6 @@ class MiniWallet:
         self.scan_tx(from_node.decoderawtransaction(tx_hex))
         return txid
 
-
 def getnewdestination(address_type='bech32m'):
     """Generate a random destination of the specified type and return the
        corresponding public key, scriptPubKey and address. Supported types are
@@ -409,23 +426,3 @@ def create_raw_chain(node, first_coin, address, privkeys, chain_length=25):
         chain_txns.append(tx)
 
     return (chain_hex, chain_txns)
-
-def bulk_transaction(tx, node, target_weight, privkeys, prevtxs=None):
-    """Pad a transaction with extra outputs until it reaches a target weight (or higher).
-    returns CTransaction object
-    """
-    tx_heavy = deepcopy(tx)
-    assert_greater_than_or_equal(target_weight, tx_heavy.get_weight())
-    while tx_heavy.get_weight() < target_weight:
-        random_spk = "6a4d0200"  # OP_RETURN OP_PUSH2 512 bytes
-        for _ in range(512*2):
-            random_spk += choice("0123456789ABCDEF")
-        tx_heavy.vout.append(CTxOut(0, bytes.fromhex(random_spk)))
-    # Re-sign the transaction
-    if privkeys:
-        signed = node.signrawtransactionwithkey(tx_heavy.serialize().hex(), privkeys, prevtxs)
-        return tx_from_hex(signed["hex"])
-    # OP_TRUE
-    tx_heavy.wit.vtxinwit = [CTxInWitness()]
-    tx_heavy.wit.vtxinwit[0].scriptWitness.stack = [CScript([OP_TRUE])]
-    return tx_heavy