Update tox to v4

Adapt to backwards-incompatible renaming.

requirements.in

@@ -6,4 +6,4 @@ sphinx<6
 sphinxcontrib-asyncio
 sphinx_rtd_theme
 types-pycurl
-tox<4
+tox

requirements.txt

@@ -12,14 +12,20 @@ black==22.12.0
     # via -r requirements.in
 build==0.10.0
     # via pip-tools
+cachetools==5.2.1
+    # via tox
 certifi==2022.12.7
     # via requests
+chardet==5.1.0
+    # via tox
 charset-normalizer==3.0.1
     # via requests
 click==8.1.3
     # via
     #   black
     #   pip-tools
+colorama==0.4.6
+    # via tox
 distlib==0.3.6
     # via virtualenv
 docutils==0.17.1
@@ -51,6 +57,7 @@ mypy-extensions==0.4.3
 packaging==23.0
     # via
     #   build
+    #   pyproject-api
     #   sphinx
     #   tox
 pathspec==0.10.3
@@ -60,25 +67,24 @@ pip-tools==6.12.1
 platformdirs==2.6.2
     # via
     #   black
+    #   tox
     #   virtualenv
 pluggy==1.0.0
     # via tox
-py==1.11.0
-    # via tox
 pycodestyle==2.10.0
     # via flake8
 pyflakes==3.0.1
     # via flake8
 pygments==2.14.0
     # via sphinx
+pyproject-api==1.5.0
+    # via tox
 pyproject-hooks==1.0.0
     # via build
 pytz==2022.7.1
     # via babel
 requests==2.28.2
     # via sphinx
-six==1.16.0
-    # via tox
 snowballstemmer==2.2.0
     # via sphinx
 sphinx==5.3.0
@@ -107,8 +113,9 @@ tomli==2.0.1
     #   black
     #   build
     #   mypy
+    #   pyproject-api
     #   tox
-tox==3.28.0
+tox==4.3.5
     # via -r requirements.in
 types-pycurl==7.45.2.0
     # via -r requirements.in

tox.ini

@@ -21,9 +21,6 @@ envlist =
         # Run the linters.
         lint
 
-# Allow shell commands in tests
-whitelist_externals = /bin/sh
-
 [testenv]
 basepython =
            py3: python3
@@ -65,6 +62,10 @@ setenv =
        {py3,py38,py39,py310,py311,pypy3}: PYTHONWARNINGS=error:::tornado
 
 
+# Allow shell commands in tests
+allowlist_externals = sh
+
+
 # All non-comment lines but the last must end in a backslash.
 # Tox filters line-by-line based on the environment name.
 commands =