René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"agent: tests that set usethis_config attributes directly must use context manager or rely on conftest reset","articleBody":"## Lesson learned from PR #1795 (infer dependencies from setup.cfg)\n\nWhen writing tests that set `usethis_config.backend` or `usethis_config.inferred_backend` directly (e.g. `usethis_config.backend = BackendEnum.poetry`), the state persists to subsequent tests because there is no cleanup. This caused spurious test failures in CI:\n\n- Tests in `TestGetProjectDeps::TestPoetry` and `TestGetDepGroups::TestPoetry` (newly added) set `usethis_config.backend = BackendEnum.poetry` directly inside a `with` block, which left `inferred_backend` stale after the test completed.\n- Subsequent tests that relied on backend auto-detection (e.g. `TestAddDepsToGroup::test_no_pyproject_toml`) received the stale `inferred_backend = poetry` and tried to call the Poetry subprocess, which is broken in the 'min dependencies' CI environment.\n- `TestGetDepGroups::TestPoetry::test_not_read_without_poetry_backend` failed because it set `backend = none` directly (not via context manager), but `inferred_backend` was already cached as `poetry` from prior tests.\n\n## Root cause\n\n`usethis_config.set(backend=...)` (the context manager) saves and restores both `backend` AND `inferred_backend`. Direct attribute assignment (`usethis_config.backend = ...`) only updates `backend`, leaving `inferred_backend` stale. `get_backend()` in `dispatch.py` checks `inferred_backend` first (line 21) before doing any detection, so stale `inferred_backend` poisons all subsequent `get_backend()` calls.\n\n## Fix applied\n\nAdded `usethis_config.backend = BackendEnum(BACKEND_DEFAULT)` and `usethis_config.inferred_backend = None` to the `clear_functools_caches` autouse fixture in `tests/conftest.py`. This ensures clean backend state at the start of each test, preventing cross-test pollution.\n\n## Recommendation\n\n- Always use `usethis_config.set(backend=...)` as a context manager in tests, not direct attribute assignment.\n- When that is not possible, rely on the autouse fixture reset now present in `tests/conftest.py`.","author":{"url":"https://github.com/nathanjmcdougall","@type":"Person","name":"nathanjmcdougall"},"datePublished":"2026-04-04T07:03:31.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/1812/usethis-python/issues/1812"}