* Improve integration test options
- Keep the platform and enable options in os.environ, don't duplicate state in utils
- Provide more user-friendly options for setting enable and platform in integration tests
* Ensure that CIBW_ENABLE is set in the test process
* Use get_enable_groups() where necessary
* feat: support pypa build
fix: update `cibuildwheel.linux.troubleshoot` to know about build
Workaround issue with PyPy venv module by installing build[virtualenv]
fix: test_dependency_constraints_file when using build
fix: test/test_pep518.py
fix: use `strtobool` to parse `CIBW_PYPA_BUILD`
fix: update `cibuildwheel.linux.troubleshoot` to know about `python -m pip wheel`
test: use `build_mode` in `test/test_dependency_versions.py` tests
* refactor: use build-backend instead
* Apply suggestions from code review
Co-authored-by: Joe Rickerby <joerick@mac.com>
* refactor: use literal types for build_frontend
* refactor(tests): build_mode -> build_frontend_env
* Update test/test_before_build.py
Co-authored-by: Joe Rickerby <joerick@mac.com>
Joe Rickerby