René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"agent: avoid creating filesystem directories with OS-special names in tests","articleBody":"## What happened\n\nA test that created a directory named `\"...\"` via `path.mkdir()` failed on Windows CI. On Windows, `\"...\"` is interpreted as parent directory traversal (`../..`), so `mkdir()` raised `FileExistsError` because the resolved path already existed. Similarly, directory names like `\"project.\"` (trailing dot) are silently stripped by Windows, leading to unexpected behaviour.\n\n## Root cause\n\nThe test created real filesystem directories to test a pure string-processing function (`get_project_name_from_dir()`). The function only reads the `.name` attribute of a `Path` object and never accesses the filesystem. By unnecessarily coupling the test to real directory creation, the test became sensitive to OS-specific path normalisation rules that are irrelevant to the logic under test.\n\n## Generalised principle\n\nWhen testing pure logic that only inspects path metadata (e.g. `.name`, `.suffix`, `.parent`) without touching the filesystem, use synthetic `Path` or `PurePosixPath` objects instead of creating real directories. This avoids cross-platform failures caused by OS-specific path restrictions — especially on Windows, where certain characters and patterns (leading/trailing dots, reserved names like `CON`, `NUL`, etc.) are invalid or silently normalised in real paths.\n\n## Recommended action\n\n- **Skill update:** Update the `usethis-python-test` skill to include guidance: \"When the code under test only reads path metadata (`.name`, `.suffix`, `.parent`) and does not access the filesystem, prefer `PurePosixPath` or direct `usethis_config.set(project_dir=...)` with synthetic paths instead of creating real directories. This avoids Windows-specific path restrictions causing test failures.\"\n- Scan the codebase for violations of this principle and fix","author":{"url":"https://github.com/nathanjmcdougall","@type":"Person","name":"nathanjmcdougall"},"datePublished":"2026-04-09T07:33:49.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/1906/usethis-python/issues/1906"}