refactor: introduce default pid file name constant in tests

Author: tdb3

test/functional/feature_filelock.py

@@ -7,7 +7,10 @@
 import string
 
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.test_node import ErrorMatch
+from test_framework.test_node import (
+    BITCOIN_PID_FILENAME_DEFAULT,
+    ErrorMatch,
+)
 
 class FilelockTest(BitcoinTestFramework):
     def add_options(self, parser):
@@ -33,7 +36,7 @@ def run_test(self):
         self.log.info("Check that cookie and PID file are not deleted when attempting to start a second bitcoind using the same datadir")
         cookie_file = datadir / ".cookie"
         assert cookie_file.exists()  # should not be deleted during the second bitcoind instance shutdown
-        pid_file = datadir / "bitcoind.pid"
+        pid_file = datadir / BITCOIN_PID_FILENAME_DEFAULT
         assert pid_file.exists()
 
         if self.is_wallet_compiled():

test/functional/test_framework/test_node.py

@@ -48,6 +48,7 @@
 NUM_XOR_BYTES = 8
 # The null blocks key (all 0s)
 NULL_BLK_XOR_KEY = bytes([0] * NUM_XOR_BYTES)
+BITCOIN_PID_FILENAME_DEFAULT = "bitcoind.pid"
 
 
 class FailedToStartError(Exception):