Use current environment instead of virtualenv for tox testenvs
The tox-current-env plugin adds two options:
- tox --current-env
- Runs the tox testenv’s commands in the current Python environment (that is, the environment where tox is invoked from and installed in). Unlike regular tox invocation, this installs no dependencies declared in deps. An attempt to run this with a Python version that doesn’t match will fail (if tox is invoked from an Python 3.7 environment, any non 3.7 testenv will fail).
- tox --print-deps-only / --print-deps-to-file
- Instead of running any commands, simply prints the declared dependencies in deps to the standard output or specified file. This is useful for preparing the current environment for the above. --print-deps-to-file will overwrite the file if it already exists.
Invoking tox without any of the above options should behave as regular tox invocation without this plugin. Any deviation from this behavior is considered a bug.
The plugin disables tox’s way of providing a testing environment, but assumes that you supply one in some other way. Always run tox with this plugin in a fresh isolated environment, such as Python virtualenv, Linux container or chroot. See other caveats below.
Obviously, tox was created to run tests in isolated Python virtual environments. The --current-env flag totally defeats the purpose of tox. Why would anybody do that, you might ask?
Well, it turns out that tox became too popular and gained another purpose.
The Python ecosystem now has formal specifications for many pieces of package metadata like versions or dependencies. However, there is no standardization yet for declaring test dependencies or running tests. The most popular de-facto standard for that today is tox, and we expect a future standard to evolve from tox.ini. This plugin lets us use tox’s dependency lists and testing commands for environments other than Python venvs.
We hope this plugin will enable community best practices around tox configuration to grow to better accomodate non-virtualenv environments in general – for example, Linux distros, Conda, or containers.
Specifically, this plugin was created for Fedora’s needs. When we package Python software as RPM packages, we try to run the project’s test suite during package build. However, we need to test if the software works integrated into Fedora, not with packages downloaded from PyPI into a fresh environment. By running the tests in current environment, we can achieve that.
If you are interested in the RPM packaging part of this, see Fedora’s %pyproject RPM macros.
Install this via pip:
$ python -m pip install tox-current-env
Or install the development version by cloning the git repository and pip-installing locally:
$ git clone https://github.com/fedora-python/tox-current-env $ cd tox-current-env $ python -m pip install -e .
When the plugin is installed, use tox with --current-env or --print-deps-only and all the other options as usual. Assuming your tox is installed on Python 3.7:
$ tox -e py37 --current-env py37 create: /home/pythonista/projects/holy-grail/tests/.tox/py37 py37 installed: ...list of packages from the current environment... py37 run-test-pre: PYTHONHASHSEED='3333333333' py37 run-test: commands... ...runs tests in current environment's Python... ___________________________________ summary ____________________________________ py37: commands succeeded congratulations :)
Attempting to run the py36 environment’s test will fail:
$ tox -e py36 --current-env py36 create: /home/pythonista/projects/holy-grail/tests/.tox/py36 ERROR: InterpreterMismatch: tox_current_env: interpreter versions do not match: in current env: (3, 7, 4, 'final', 0) requested: (3, 6, 9, 'final', 0) ___________________________________ summary ____________________________________ ERROR: py36: InterpreterMismatch: tox_current_env: interpreter versions do not match: in current env: (3, 7, 4, 'final', 0) requested: (3, 6, 9, 'final', 0)
To get list of test dependencies, run:
$ tox -e py37 --print-deps-only py37 create: /home/pythonista/projects/holy-grail/tests/.tox/py37 py37 installed: ...you can see almost anything here... py37 run-test-pre: PYTHONHASHSEED='3333333333' dep1 dep2 ... ___________________________________ summary ____________________________________ py37: commands succeeded congratulations :)
Caveats, warnings and limitations
Use an isolated environment
Running (especially third party software’s) tests in your system Python environment is dangerous. Always use this plugin in an isolated environment, such as Python virtualenv, Linux container, virtual machine or chroot. You have been warned.
Do not rely on virtualenv details
In order to support the python command in the commands section, the current environment invocation of tox creates a fake virtual environment that just has a symbolic link to the Python executable. The link is named python even if the real interpreter’s name is different (such as python3.7 or pypy). Any other commands are not linked anywhere and it is the users’ responsibility to make sure such commands are in $PATH and use the correct Python. This can lead to slightly different results of tests than invoking them directly, especially if you have assumptions about sys.executable or other commands in your tests.
As a specific example, tests should invoke python -m pytest rather than assuming the pytest command is present and uses the correct version of Python.
Don’t mix current-env and regular tox runs
Tox caches the virtualenvs it creates, and doesn’t distinguish between regular virtualenvs and --current-env. Don’t mix tox --current-env or tox --print-deps-only runs and regular tox runs (without the flag). If you ever need to do this, use tox’s --recreate/-r flag to clear the cache.
The plugin should abort with a meaningful error message if this is detected, but in some cases (such as running tox --current-env, uninstalling the plugin, and running tox), you will get undefined results (such as installing packages from PyPI into your current environment).
Environment variables are not passed by default
Although the plugin name suggests that current environment is used for tests, it means the Python environment, not Shell. If you want the tests to see environment variables of the calling process, use the TOX_TESTENV_PASSENV environment variable. Read the documentation for passing environment variables to tox.
Other limitations and known bugs
The installed: line in the output of tox --print-deps-only shows irrelevant output (based on the content of the real or faked virtual environment).
Regardless of any Python flags used in the shebang of tox, the tests are invoked with sys.executable without any added flags (unless explicitly invoked with them in the commands section).
The current environment’s Python is tested for the major and minor version only. Different interpreters with the same Python version (such as CPython and PyPy) are treated as equal.
Only Linux is supported, with special emphasis on Fedora. This plugin might work on other Unix-like systems, but does not work on Microsoft Windows.
This is alpha quality software. Use it at your on your own risk. Pull requests with improvements are welcome.
Development, issues, support
In order to run the tests, you’ll need tox and Python 3.6, 3.7 and 3.8 installed. The integration tests assume all three are available. On Fedora, you just need to dnf install tox.
Run tox to invoke the tests.
Running tests of this plugin with its own --current-env flag will most likely blow up.
The tox-current-env project is licensed under the so-called MIT license, full text available in the LICENSE file.
Code of Conduct
The tox-current-env project follows the Fedora’s Code of Conduct.
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