[Test] Fix path tests on windows

[citelao]

Description

Fixes #5802.

Today, tests fail on most Windows machines because we hard-code D: as the root drive, but most machines use C:. This change uses the same normalization function in the test assertion to ensure the drives match.

To Do

• Documentation.
• Changelog.
• Tests. (this is a tests change)

What changed?

• Updated tests to generate the drive name via normalization, instead of hard-coding D:.
• Updated the Item::destination() method to document the relative_to_libdir param.

How tested?

• Tests pass locally.

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[Copilot]

Pull Request Overview

This pull request fixes Windows path tests by replacing the hard-coded drive letter "D:" with the system drive value fetched dynamically from the environment.

• Replaces hard-coded "D:" with os.environ.get("SystemDrive", "C:") in test assertions.
• Improves documentation of the destination method in the library module.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
test/test_library.py	Updates to Windows path handling in tests and declaration of instance variables.
beets/library.py	Updates the docstring to clarify behavior when the relative_to_libdir parameter is true.

[citelao]

Hmm... this D:/ seems to be unrelated to the system drive. I bet it's a specific drive for Github Actions...

[citelao]

Hmm... this D:/ seems to be unrelated to the system drive. I bet it's a specific drive for Github Actions...

Root-caused: Item::destination() relies on util.normpath, which calls os.path.abspath, which relies on your current working directory (cwd). I bet the cwd in our tests happens to be D:.

[semohr]

Thank you for the quick fix and find!

Funny that the drive was hardcoded, I guess not too many people run the tests on a local windows machine.

Could you add a changelog entry? Other than that, should be ready to merge.

[citelao]

Happy to help! Changelog pushed.