tests: use `test -f` instead of `ls` to see if a file is present (issue6662) ls's exit code when file doesn't exist is 2 on Linux and 1 on NetBSD, so let's use something that's supposedly more portable, since we only care whether the file is there or not.

[build-system]
requires = ["setuptools", "wheel"]

[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true