Improve contributing instructions

CONTRIBUTING.md

@@ -7,7 +7,25 @@ still need proper phrasing - if you'd like to help - be sure to make a PR.
 Please know that we do appreciate all contributions - bug reports as well as
 Pull Requests.
 
-## PR Merge Criteria
+## Setting up a development environment and running tests
+
+After you've cloned the repository,
+
+1. Set up a Python virtualenv (the methods vary depending on tooling and operating system)
+  and activate it.
+2. Install Babel in editable mode with development dependencies: `pip install -e .[dev]`
+3. Run `make import-cldr` to import the CLDR database.
+  This will download the CLDR database and convert it to a format that Babel can use.
+4. Run `make test` to run the tests. You can also run e.g. `pytest --cov babel .` to
+   run the tests with coverage reporting enabled.
+
+You can also use [Tox][tox] to run the tests in separate virtualenvs
+for all supported Python versions; a `tox.ini` configuration (which is what the CI process
+uses) is included in the repository.
+
+## On pull requests
+
+### PR Merge Criteria
 
 For a PR to be merged, the following statements must hold true:
 
@@ -19,14 +37,16 @@ For a PR to be merged, the following statements must hold true:
 To begin contributing have a look at the open [easy issues](https://github.com/python-babel/babel/issues?q=is%3Aopen+is%3Aissue+label%3Adifficulty%2Flow)
 which could be fixed.
 
-## Correcting PRs
+### Correcting PRs
 
 Rebasing PRs is preferred over merging master into the source branches again
 and again cluttering our history. If a reviewer has suggestions, the commit
 shall be amended so the history is not cluttered by "fixup commits".
 
-## Writing Good Commits
+### Writing Good Commits
 
 Please see
 https://api.coala.io/en/latest/Developers/Writing_Good_Commits.html
 for guidelines on how to write good commits and proper commit messages.
+
+[tox]: https://tox.wiki/en/latest/

Makefile

@@ -1,18 +1,7 @@
 test: import-cldr
 	python ${PYTHON_TEST_FLAGS} -m pytest ${PYTEST_FLAGS}
 
-test-env:
-	virtualenv test-env
-	test-env/bin/pip install pytest
-	test-env/bin/pip install --editable .
-
-clean-test-env:
-	rm -rf test-env
-
-standalone-test: import-cldr test-env
-	test-env/bin/pytest tests ${PYTEST_FLAGS}
-
-clean: clean-cldr clean-pyc clean-test-env
+clean: clean-cldr clean-pyc
 
 import-cldr:
 	python scripts/download_import_cldr.py
@@ -28,7 +17,7 @@ clean-pyc:
 develop:
 	pip install --editable .
 
-tox-test: import-cldr
+tox-test:
 	tox
 
-.PHONY: test develop tox-test clean-pyc clean-cldr import-cldr clean clean-test-env standalone-test
+.PHONY: test develop tox-test clean-pyc clean-cldr import-cldr clean standalone-test

setup.py

@@ -67,6 +67,13 @@ def run(self):
         # Python 3.9 and later include zoneinfo which replaces pytz
         'pytz>=2015.7; python_version<"3.9"',
     ],
+    extras_require={
+        'dev': [
+            'pytest>=6.0',
+            'pytest-cov',
+            'freezegun~=1.0',
+        ],
+    },
     cmdclass={'import_cldr': import_cldr},
     zip_safe=False,
     # Note when adding extractors: builtin extractors we also want to

tox.ini

@@ -5,10 +5,9 @@ envlist =
     py{37,38}-pytz
 
 [testenv]
+extras =
+    dev
 deps =
-    pytest>=6.0
-    pytest-cov
-    freezegun==0.3.12
     backports.zoneinfo;python_version<"3.9"
     tzdata;sys_platform == 'win32'
     pytz: pytz