diff --git a/test/functional/feature_help.py b/test/functional/feature_help.py
--- a/test/functional/feature_help.py
+++ b/test/functional/feature_help.py
@@ -3,7 +3,6 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Verify that starting bitcoin with -h works as expected."""
-import subprocess
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import assert_equal
@@ -18,46 +17,48 @@
         self.add_nodes(self.num_nodes)
         # Don't start the node
 
+    def get_node_output(self, *, ret_code_expected):
+        ret_code = self.nodes[0].process.wait(timeout=5)
+        assert_equal(ret_code, ret_code_expected)
+        self.nodes[0].stdout.seek(0)
+        self.nodes[0].stderr.seek(0)
+        out = self.nodes[0].stdout.read()
+        err = self.nodes[0].stderr.read()
+        self.nodes[0].stdout.close()
+        self.nodes[0].stderr.close()
+
+        # Clean up TestNode state
+        self.nodes[0].running = False
+        self.nodes[0].process = None
+        self.nodes[0].rpc_connected = False
+        self.nodes[0].rpc = None
+
+        return out, err
+
     def run_test(self):
         self.log.info("Start bitcoin with -h for help text")
-        self.nodes[0].start(extra_args=['-h'],
-                            stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+        self.nodes[0].start(extra_args=['-h'])
         # Node should exit immediately and output help to stdout.
-        ret_code = self.nodes[0].process.wait(timeout=1)
-        assert_equal(ret_code, 0)
-        output = self.nodes[0].process.stdout.read()
+        output, _ = self.get_node_output(ret_code_expected=0)
         assert b'Options' in output
         self.log.info("Help text received: {} (...)".format(output[0:60]))
-        self.nodes[0].running = False
 
         self.log.info("Start bitcoin with -version for version information")
-        self.nodes[0].start(extra_args=['-version'],
-                            stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+        self.nodes[0].start(extra_args=['-version'])
         # Node should exit immediately and output version to stdout.
-        ret_code = self.nodes[0].process.wait(timeout=1)
-        assert_equal(ret_code, 0)
-        output = self.nodes[0].process.stdout.read()
+        output, _ = self.get_node_output(ret_code_expected=0)
         assert b'version' in output
         self.log.info("Version text received: {} (...)".format(output[0:60]))
 
         # Test that arguments not in the help results in an error
         self.log.info(
             "Start bitcoind with -fakearg to make sure it does not start")
-        self.nodes[0].start(extra_args=['-fakearg'],
-                            stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+        self.nodes[0].start(extra_args=['-fakearg'])
         # Node should exit immediately and output an error to stderr
-        ret_code = self.nodes[0].process.wait(timeout=1)
-        assert_equal(ret_code, 1)
-        output = self.nodes[0].process.stderr.read()
+        _, output = self.get_node_output(ret_code_expected=1)
         assert b'Error parsing command line arguments' in output
         self.log.info("Error message received: {} (...)".format(output[0:60]))
 
-        # Clean up TestNode state
-        self.nodes[0].running = False
-        self.nodes[0].process = None
-        self.nodes[0].rpc_connected = False
-        self.nodes[0].rpc = None
-
 
 if __name__ == '__main__':
     HelpTest().main()
diff --git a/test/functional/rpc_users.py b/test/functional/rpc_users.py
--- a/test/functional/rpc_users.py
+++ b/test/functional/rpc_users.py
@@ -4,13 +4,14 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test multiple RPC users."""
 
+import configparser
 import http.client
 import os
-import urllib.parse
-import subprocess
 from random import SystemRandom
 import string
-import configparser
+import subprocess
+import sys
+import urllib.parse
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
@@ -37,7 +38,7 @@
         config = configparser.ConfigParser()
         config.read_file(open(self.options.configfile, encoding='utf-8'))
         gen_rpcauth = config['environment']['RPCAUTH']
-        p = subprocess.Popen([gen_rpcauth, self.user],
+        p = subprocess.Popen([sys.executable, gen_rpcauth, self.user],
                              stdout=subprocess.PIPE, universal_newlines=True)
         lines = p.stdout.read().splitlines()
         rpcauth3 = lines[1]
diff --git a/test/functional/test_framework/test_node.py b/test/functional/test_framework/test_node.py
--- a/test/functional/test_framework/test_node.py
+++ b/test/functional/test_framework/test_node.py
@@ -190,8 +190,8 @@
             self.default_args = [def_arg for def_arg in self.default_args
                                  if rm_arg != def_arg and not def_arg.startswith(rm_arg + '=')]
 
-    def start(self, extra_args=None, stdout=None,
-              stderr=None, *args, **kwargs):
+    def start(self, extra_args=None, *, stdout=None,
+              stderr=None, **kwargs):
         """Start the node."""
         if extra_args is None:
             extra_args = self.extra_args
@@ -223,7 +223,6 @@
             env=subp_env,
             stdout=stdout,
             stderr=stderr,
-            *args,
             **kwargs)
 
         self.running = True
@@ -299,6 +298,9 @@
             raise AssertionError(
                 "Unexpected stderr {} != {}".format(stderr, expected_stderr))
 
+        self.stdout.close()
+        self.stderr.close()
+
         del self.p2ps[:]
 
     def is_node_stopped(self):