diff --git a/src/charm.py b/src/charm.py
index 2d1b077..bdc5030 100755
--- a/src/charm.py
+++ b/src/charm.py
@@ -149,5 +149,6 @@ class OpenstackLoadbalancerCharm(ops_openstack.core.OSBaseCharm):
         self._configure_haproxy()
         self._send_loadbalancer_response()
 
+
 if __name__ == "__main__":
     main(OpenstackLoadbalancerCharm)
diff --git a/tox.ini b/tox.ini
index c855061..7bb995e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,22 +7,6 @@ skipsdist = True
 sitepackages = False
 # NOTE: Avoid false positives by not skipping missing interpreters.
 skip_missing_interpreters = False
-# NOTES:
-# * We avoid the new dependency resolver by pinning pip < 20.3, see
-#   https://github.com/pypa/pip/issues/9187
-# * Pinning dependencies requires tox >= 3.2.0, see
-#   https://tox.readthedocs.io/en/latest/config.html#conf-requires
-# * It is also necessary to pin virtualenv as a newer virtualenv would still
-#   lead to fetching the latest pip in the func* tox targets, see
-#   https://stackoverflow.com/a/38133283
-# * It is necessary to declare setuptools as a dependency otherwise tox will
-#   fail very early at not being able to load it. The version pinning is in
-#   line with `pip.sh`.
-requires = pip < 20.3
-           virtualenv < 20.0
-           setuptools < 50.0.0
-# NOTE: https://wiki.canonical.com/engineering/OpenStack/InstallLatestToxOnOsci
-minversion = 3.2.0
 
 [testenv]
 setenv = VIRTUAL_ENV={envdir}
@@ -37,7 +21,12 @@ allowlist_externals =
     bash
     charmcraft
     rename.sh
-passenv = HOME TERM CS_* OS_* TEST_*
+passenv =
+    HOME
+    TERM
+    CS_*
+    OS_*
+    TEST_*
 deps = -r{toxinidir}/test-requirements.txt
 
 [testenv:py35]
@@ -77,8 +66,8 @@ deps = -r{toxinidir}/requirements.txt
 
 [testenv:pep8]
 basepython = python3
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps = flake8==7.1.1
+       git+https://github.com/juju/charm-tools.git
 commands = flake8 {posargs} src unit_tests tests
 
 [testenv:cover]
diff --git a/unit_tests/test_openstack_loadbalancer_charm.py b/unit_tests/test_openstack_loadbalancer_charm.py
index 746b41a..7f1c6bd 100644
--- a/unit_tests/test_openstack_loadbalancer_charm.py
+++ b/unit_tests/test_openstack_loadbalancer_charm.py
@@ -16,6 +16,7 @@
 
 import ipaddress
 import json
+import os
 import re
 import sys
 import unittest
@@ -25,7 +26,9 @@ sys.path.append('src')  # noqa
 
 from mock import patch
 
-from ops.testing import Harness, _TestingModelBackend
+from ops._private.harness import _TestingModelBackend
+from ops.jujucontext import _JujuContext
+from ops.testing import Harness
 from ops import framework, model
 import charm
 from unit_tests.manage_test_relations import (
@@ -72,6 +75,8 @@ class TestOpenstackLoadbalancerCharmBase(CharmTestCase):
 
     def get_harness(self):
         initial_config = {}
+        # dummy juju version
+        os.environ["JUJU_VERSION"] = "0.0.0"
         _harness = Harness(
             _OpenstackLoadbalancerCharm,
             meta='''
@@ -122,7 +127,10 @@ requires:
                 return network_data[endpoint_name]
 
         _harness._backend = _TestingOPSModelBackend(
-            _harness._unit_name, _harness._meta)
+            _harness._unit_name,
+            _harness._meta,
+            _harness._get_config(None),
+            _JujuContext.from_dict(os.environ),)
         _harness._model = model.Model(
             _harness._meta,
             _harness._backend)