diff --git a/src/allmydata/test/test_node.py b/src/allmydata/test/test_node.py
index cf5fa27f3..c6cff1bab 100644
--- a/src/allmydata/test/test_node.py
+++ b/src/allmydata/test/test_node.py
@@ -69,6 +69,8 @@ import allmydata.test.common_util as testutil
 
 from .common import (
     ConstantAddresses,
+    SameProcessStreamEndpointAssigner,
+    UseNode,
 )
 
 def port_numbers():
@@ -80,11 +82,10 @@ class LoggingMultiService(service.MultiService):
 
 
 # see https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2946
-def testing_tub(config_data=''):
+def testing_tub(reactor, config_data=''):
     """
     Creates a 'main' Tub for testing purposes, from config data
     """
-    from twisted.internet import reactor
     basedir = 'dummy_basedir'
     config = config_from_string(basedir, 'DEFAULT_PORTNUMFILE_BLANK', config_data)
     fileutil.make_dirs(os.path.join(basedir, 'private'))
@@ -112,6 +113,9 @@ class TestCase(testutil.SignalMixin, unittest.TestCase):
         # try to bind the port.  We'll use a low-numbered one that's likely to
         # conflict with another service to prove it.
         self._available_port = 22
+        self.port_assigner = SameProcessStreamEndpointAssigner()
+        self.port_assigner.setUp()
+        self.addCleanup(self.port_assigner.tearDown)
 
     def _test_location(
             self,
@@ -137,11 +141,23 @@ class TestCase(testutil.SignalMixin, unittest.TestCase):
         :param local_addresses: If not ``None`` then a list of addresses to
             supply to the system under test as local addresses.
         """
+        from twisted.internet import reactor
+
         basedir = self.mktemp()
         create_node_dir(basedir, "testing")
+        if tub_port is None:
+            # Always configure a usable tub.port address instead of relying on
+            # the automatic port assignment.  The automatic port assignment is
+            # prone to collisions and spurious test failures.
+            _, tub_port = self.port_assigner.assign(reactor)
+
         config_data = "[node]\n"
-        if tub_port:
-            config_data += "tub.port = {}\n".format(tub_port)
+        config_data += "tub.port = {}\n".format(tub_port)
+
+        # If they wanted a certain location, go for it.  This probably won't
+        # agree with the tub.port value we set but that only matters if
+        # anything tries to use this to establish a connection ... which
+        # nothing in this test suite will.
         if tub_location is not None:
             config_data += "tub.location = {}\n".format(tub_location)
 
@@ -149,7 +165,7 @@ class TestCase(testutil.SignalMixin, unittest.TestCase):
             self.patch(iputil, 'get_local_addresses_sync',
                        lambda: local_addresses)
 
-        tub = testing_tub(config_data)
+        tub = testing_tub(reactor, config_data)
 
         class Foo(object):
             pass
@@ -431,7 +447,12 @@ class TestCase(testutil.SignalMixin, unittest.TestCase):
 
     @defer.inlineCallbacks
     def test_logdir_is_str(self):
-        basedir = "test_node/test_logdir_is_str"
+        from twisted.internet import reactor
+
+        basedir = FilePath(self.mktemp())
+        fixture = UseNode(None, None, basedir, "pb://introducer/furl", {}, reactor=reactor)
+        fixture.setUp()
+        self.addCleanup(fixture.cleanUp)
 
         ns = Namespace()
         ns.called = False
@@ -440,8 +461,7 @@ class TestCase(testutil.SignalMixin, unittest.TestCase):
             self.failUnless(isinstance(logdir, str), logdir)
         self.patch(foolscap.logging.log, 'setLogDir', call_setLogDir)
 
-        create_node_dir(basedir, "nothing to see here")
-        yield client.create_client(basedir)
+        yield fixture.create_node()
         self.failUnless(ns.called)
 
     def test_set_config_unescaped_furl_hash(self):