DEVELOPMENT SUPPORT: Fix tox for python 2.7

* Need to use "pip install --user ..." for now
* Scripts seem no longer to be installed

HINT: Seems to be related to virtualenv and macOS 12 Monterey
SEE:  pypa/virtualenv#2284

tox.ini

@@ -8,18 +8,20 @@
 #
 #   Run tox, like:
 #
-#       tox -e py27
-#       tox -e py37
+#   tox -e py27     # Runs tox with python 2.7
+#   tox -e py39     # Runs tox with python 3.9
+#   tox             # Runs tox with all installed python versions.
+#   tox --parallel  # Runs tox in parallel mode w/ all envs.
 #
 # SEE ALSO:
-#   * https://tox.readthedocs.io/en/latest/config.html
+# * https://tox.readthedocs.io/en/latest/config.html
 # ============================================================================
 # -- ONLINE USAGE:
 # PIP_INDEX_URL = https://pypi.org/simple
 
 [tox]
 minversion = 3.10.0
-envlist    = py39, py310, py38, pypy, pypy3, doctest
+envlist    = py39, py27, py310, py38, pypy, pypy3, doctest
 skip_missing_interpreters = True
 sitepackages = False
 indexserver =
@@ -44,19 +46,29 @@ setenv =
     PYSETUP_BOOTSTRAP = no
 
 
-# -- HINT: "pytest" script is no longer installed for Python 2.7.
-# XFAIL: tox -e py27  -- Due to a pip install problem (disabled in: envlist).
+# -- SPECIAL CASE:
+# RELATED: https://github.com/pypa/virtualenv/issues/2284 -- macOS 12 Monterey related
+# NOTES:
+#  * pip-install seems to need "--user" option.
+#  * Script(s) do not seem to be installed any more (actually to $HOME/User area).
 [testenv:py27]
+install_command = pip install --user -U {opts} {packages}
 changedir = {toxinidir}
-commands =
-    pytest {posargs:tests}
-deps =
+commands=
+    python -m pytest {posargs:tests}
+deps=
     {[testenv]deps}
-setenv =
-    PYTHONPATH={toxinidir}
-    TOXRUN = yes
-    PYSETUP_BOOTSTRAP = no
+passenv =
+     PYTHONPATH = {toxinidir}
+# MAYBE: allowlist_externals = curl
+
 
+# -- VIRTUAL-ENVIRONMENT SETUP PROCEDURE: For python 2.7
+#   virtualenv -p python2.7 .venv_py27
+#   source .venv_py27
+#   scripts/ensurepip_python27.sh
+#   python -m pip install -r py.requirements/basic.txt
+#   python -m pip install -r py.requirements/testing.txt
 
 [testenv:doctest]
 basepython = python3