Add testenv:dev to create development environment (#765)

docs/contributing.rst

@@ -11,36 +11,35 @@ mailing list`_, to ask questions or get involved.
 Getting started
 ---------------
 
-We recommend you use a `virtual environment`_, so that twine and its
-dependencies do not interfere with other packages installed on your
-machine.
-
-Clone the twine repository from GitHub, then make and activate a
-virtual environment that uses Python 3.6 or newer as the default
-Python. For example:
+We use `tox`_ to run tests, check code style, and build the documentation.
+To install ``tox``, run:
 
 .. code-block:: console
 
-    cd /path/to/your/local/twine
-    python3.6 -m venv venv
-    source venv/bin/activate
+    python3 -m pip install tox
 
-Then, run the following commands:
+Clone the twine repository from GitHub, then run:
 
 .. code-block:: console
 
-    pip install -U pip
-    pip install -e .
+    cd /path/to/your/local/twine
+    tox -e dev
 
-Now, in your virtual environment, ``twine`` is pointing at your local copy, so
-when you make changes, you can easily see their effect.
+This creates a `virtual environment`_, so that twine and its
+dependencies do not interfere with other packages installed on your
+machine. In the virtual environment, ``twine`` is pointing at your
+local copy, so when you make changes, you can easily see their effect.
 
-We use `tox`_ to run tests, check code style, and build the documentation.
-To install ``tox`` in your active virtual environment, run:
+The virtual environment also contains the tools for running tests
+and checking code style, so you can run them on single files directly or
+in your code editor. However, we still encourage using the ``tox`` commands
+below on the whole codebase.
+
+To use the virtual environment, run:
 
 .. code-block:: console
 
-    pip install tox
+    source venv/bin/activate
 
 Building the documentation
 ^^^^^^^^^^^^^^^^^^^^^^^^^^

tox.ini

@@ -102,6 +102,21 @@ commands =
     python -m build
     python -m twine upload dist/*
 
+[testenv:dev]
+envdir = {posargs:venv}
+recreate = True
+deps =
+    {[testenv]deps}
+    {[testenv:integration]deps}
+    {[testenv:format]deps}
+    {[testenv:lint]deps}
+    {[testenv:types]deps}
+download = True
+usedevelop = True
+commands =
+    python -c 'import sys; print(sys.executable)'
+    python --version
+
 [testenv:devpi]
 deps =
     devpi-server