fix(tests): spawn servers via sys.executable

[mgorny]

Summary of Changes

Spawn the servers (gunicorn, uvicorn, etc.) during tests through sys.executable rather than directly, in order to ensure that the test server is run using the same Python executable as the test suite. Otherwise, the test servers are started using the Python executable specified in their shebang and can therefore escape the virtualenv they are being run in.

This is particularly problem for tests being run from Gentoo ebuilds. We create a --system-site-packages venv to install falcon in, in order to test whether it works correctly against the dependencies installed on the system prior to installing it. However, the installed packages such as gunicorn specify /usr/bin/python* shebangs that override the venv and therefore make these servers unable to find venv-installed falcon. Running them via sys.executable ensures that they are started through Python installed in the venv.

Related Issues

n/a

Pull Request Checklist

• [x] Applied changes to both WSGI and ASGI code paths and interfaces (where applicable).
• [x] Added tests for changed code.
• [x] Prefixed code comments with GitHub nick and an appropriate prefix.
• [x] Coding style is consistent with the rest of the framework.
• [x] Updated documentation for changed code.
  • [x] Added docstrings for any new classes, functions, or modules.
  • [x] Updated docstrings for any modifications to existing code.
  • [x] Updated both WSGI and ASGI docs (where applicable).
  • [x] Added references to new classes, functions, or modules to the relevant RST file under docs/.
  • [x] Updated all relevant supporting documentation files under docs/.
  • [x] A copyright notice is included at the top of any new modules (using your own name or the name of your organization).
  • [x] Changed/added classes/methods/functions have appropriate versionadded, versionchanged, or deprecated directives.
• [x] Changes (and possible deprecations) have towncrier news fragments under docs/_newsfragments/, with the file name format {issue_number}.{fragment_type}.rst. (Run towncrier --draft to ensure it renders correctly.)

[codecov[bot]]

Codecov Report

Merging #2047 (b367e85) into master (0066cb1) will not change coverage. The diff coverage is n/a.

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  Lines         6707      6707           
  Branches      1238      1238           
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  Hits          6707      6707           

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[mgorny]

Heh I actually had this problem myself for uWSGI because I had that globally on my system, but it is unfortunately a harder task.

Yeah, I couldn't figure out how to make this work for uwsgi.

I'm thinking to myself though whether we shouldn't apply the same treatment for uvicorn for consistency too then?

Hmm, I did uvicorn in test_wsgi_servers but I see it's also in test_asgi_servers. I'll update the PR in a minute.

[mgorny]

Covered asgi tests now too.

[mgorny]

Well, I'm running a pretty big test environment here and gunicorn etc. just happen to be installed on the system. The goal's pretty much to try and see what could break on production systems — and I suppose people tend to run webservers there ;-).