fix: inaccurate Python instructions

[wesleyboar]

Overview

Fixed order and description of instructions for "Testing" "via Python".

Changes

• moved pip install poetry to its own group
• moved poetry install before poetry shell
• changed instruction groups and descriptions

Notes

The poetry install and poetry shell commands both activate a Poetry-managed virtual environment, which is helpful to avoid dependency conflicts for users who do not use virtual environments to isolate their projects.

The poetry install installs project dependencies within the current virtual environment. The python shell allows running commands for installed dependencies e.g. mkdocs within the current virtual environment.

If poetry install has not been run yet, then poetry shell would not offer mkdocs. When mkdocs is unavailable, user response may be to install mkdocs. Installing mkdocs, while in this state, can cause different problems depending on how it is done.

• pip install mkdocs would install latest version, not project version.
• poetry install(…) would fail.[^1]

[^1]: Because poetry is not installed within the virtual environment, because poetry is not a dependency of the project itself.