Move the create_empty_fork method to the test framework's blocktools.py module to enable reuse across multiple tests.

diff --git a/test/functional/mempool_updatefromblock.py b/test/functional/mempool_updatefromblock.py
index 060c72e2..0340bb74 100755
--- a/test/functional/mempool_updatefromblock.py
+++ b/test/functional/mempool_updatefromblock.py
@@ -11,10 +11,7 @@ from decimal import Decimal
 from math import ceil
 import time
 
-from test_framework.blocktools import (
-    create_block,
-    create_coinbase,
-)
+from test_framework.blocktools import create_empty_fork
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import assert_equal, assert_raises_rpc_error
 from test_framework.wallet import MiniWallet
@@ -30,26 +27,6 @@ class MempoolUpdateFromBlockTest(BitcoinTestFramework):
         self.num_nodes = 1
         self.extra_args = [['-limitclustersize=1000']]
 
-    def create_empty_fork(self, fork_length):
-        '''
-            Creates a fork using first node's chaintip as the starting point.
-            Returns a list of blocks to submit in order.
-        '''
-        tip = int(self.nodes[0].getbestblockhash(), 16)
-        height = self.nodes[0].getblockcount()
-        block_time = self.nodes[0].getblock(self.nodes[0].getbestblockhash())['time'] + 1
-
-        blocks = []
-        for _ in range(fork_length):
-            block = create_block(tip, create_coinbase(height + 1), block_time)
-            block.solve()
-            blocks.append(block)
-            tip = block.hash_int
-            block_time += 1
-            height += 1
-
-        return blocks
-
     def transaction_graph_test(self, size, *, n_tx_to_mine, fee=100_000):
         """Create an acyclic tournament (a type of directed graph) of transactions and use it for testing.
 
@@ -69,7 +46,7 @@ class MempoolUpdateFromBlockTest(BitcoinTestFramework):
 
         # Prep for fork with empty blocks to not use invalidateblock directly
         # for reorg case. The rpc has different codepath
-        fork_blocks = self.create_empty_fork(fork_length=7)
+        fork_blocks = create_empty_fork(self.nodes[0], fork_length=7)
 
         tx_id = []
         tx_size = []
@@ -146,7 +123,7 @@ class MempoolUpdateFromBlockTest(BitcoinTestFramework):
         assert_equal(self.nodes[0].getrawmempool(), [])
 
         # Set up empty fork blocks ahead of time, needs to be longer than full fork made later
-        fork_blocks = self.create_empty_fork(fork_length=60)
+        fork_blocks = create_empty_fork(self.nodes[0], fork_length=60)
 
         large_std_txs = []
         # Add children to ensure they're recursively removed if disconnectpool trimming of parent occurs
@@ -195,7 +172,7 @@ class MempoolUpdateFromBlockTest(BitcoinTestFramework):
         assert_equal(self.nodes[0].getrawmempool(), [])
 
         # Prep fork
-        fork_blocks = self.create_empty_fork(fork_length=10)
+        fork_blocks = create_empty_fork(self.nodes[0])
 
         # Two higher than descendant count
         chain = wallet.create_self_transfer_chain(chain_length=DEFAULT_CLUSTER_LIMIT + 2)
diff --git a/test/functional/test_framework/blocktools.py b/test/functional/test_framework/blocktools.py
index eb1d3b05..605e9102 100644
--- a/test/functional/test_framework/blocktools.py
+++ b/test/functional/test_framework/blocktools.py
@@ -84,6 +84,9 @@ assert_equal(uint256_from_compact(DIFF_4_N_BITS), DIFF_4_TARGET)
 # From BIP325
 SIGNET_HEADER = b"\xec\xc7\xda\xa2"
 
+# Number of blocks to create in temporary blockchain branch for reorg testing
+FORK_LENGTH = 10
+
 def nbits_str(nbits):
     return f"{nbits:08x}"
 
@@ -113,6 +116,26 @@ def create_block(hashprev=None, coinbase=None, ntime=None, *, version=None, tmpl
     block.hashMerkleRoot = block.calc_merkle_root()
     return block
 
+def create_empty_fork(node, fork_length=FORK_LENGTH):
+    '''
+        Creates a fork using node's chaintip as the starting point.
+        Returns a list of blocks to submit in order.
+    '''
+    tip = int(node.getbestblockhash(), 16)
+    height = node.getblockcount()
+    block_time = node.getblock(node.getbestblockhash())['time'] + 1
+
+    blocks = []
+    for _ in range(fork_length):
+        block = create_block(tip, create_coinbase(height + 1), block_time)
+        block.solve()
+        blocks.append(block)
+        tip = block.hash_int
+        block_time += 1
+        height += 1
+
+    return blocks
+
 def get_witness_script(witness_root, witness_nonce):
     witness_commitment = hash256(ser_uint256(witness_root) + ser_uint256(witness_nonce))
     output_data = WITNESS_COMMITMENT_HEADER + witness_commitment