test-conventions-claude-config

Filesystem fixtures must not collide under case-insensitive filesystems

CI runs Linux only (.github/workflows/tests.yml), and contributors run the same
suite on macOS, whose default volume is case-insensitive and case-preserving. Two
paths in one directory that differ only by case are one path there. A second
mkdir() raises FileExistsError, a second write_text() silently overwrites the
first, and exists() returns True for the wrong case — on a contributor's machine,
never in CI.

No two entries in one fixture directory may address the same file on a
case-insensitive volume, and a test must not rely on exists() telling
case-only-different names apart. Names equal under str.casefold() are the case
to check for.

When a test builds a path from a value set — a loop, a parametrize list, a
factory helper's name argument — check the set for a casefold pair. If it has
one, give each value its own tmp_path via @pytest.mark.parametrize and keep
the directory name itself constant.