Add tox for local development testing

This tox setup is mostly intended to execute python3.9 and python3.12 in
our local setup without the need of waiting for CI to run the specific
test.

Makefile

@@ -36,5 +36,5 @@ clean: ## Clean project files
 	@find . -name '__pycache__' -exec rm -fr {} +
 	@find . -name '*.pyc' -exec rm -f {} +
 	@find . -name '*.pyo' -exec rm -f {} +
-	@rm -rf .pdm-build .ruff_cache .coverage .pdm-python dist
+	@rm -rf .pdm-build .ruff_cache .coverage .pdm-python dist .tox
 	@coverage erase

pyproject.toml

@@ -54,16 +54,6 @@ lint.ignore = [
 [tool.pdm]
 distribution = true
 
-[tool.pdm.dev-dependencies]
-dev = [
-    "pytest==8.3.3",
-    "pytest-cov==6.0.0",
-    "pytest-randomly==3.16.0",
-    "coverage==7.6.4",
-    "pytest-sugar==1.0.0",
-    "pytest-clarity==1.0.1",
-]
-
 [tool.pdm.scripts]
 unit-test = "pdm run make unit-test"
 coverage = "pdm run make coverage"
@@ -79,3 +69,6 @@ skip_empty = true
 [tool.coverage.run]
 branch = true
 source = ["command_line_assistant"]
+
+[dependency-groups]
+dev = ["pytest==8.3.3", "pytest-cov==6.0.0", "pytest-randomly==3.16.0", "coverage==7.6.4", "pytest-sugar==1.0.0", "pytest-clarity==1.0.1", "tox>=4.23.2", "tox-pdm>=0.7.2"]

tox.ini

@@ -0,0 +1,13 @@
+[tox]
+envlist = py3{9,12}
+isolated_build = true
+
+[testenv]
+setenv =
+    # Ignore the python version defined in .pdm-python
+    PDM_IGNORE_SAVED_PYTHON='1'
+groups =
+    dev
+allowlist_externals = pdm
+# Execute pdm run unit-test
+commands = unit-test {posargs}