feat: add ruff linter with ci check

Liniting the python files in tests directory would reduce whitespace etc
change and enforce basic coding standard for those. Kind of
opportunistic PR as there might be other opinions about how to deal with
this.

Author: oikarinen

.github/workflows/ci.yml

@@ -27,6 +27,8 @@ jobs:
 
           readarray -t changed_files <<<"$(jq -r '.[]' <<<'${{ steps.files.outputs.added_modified }}')"
           ~/go/bin/editorconfig-checker ${changed_files[@]}
+      - name: Lint and format Python with Ruff
+        uses: astral-sh/ruff-action@v1
 
   typo:
     runs-on: ubuntu-latest

tests/pyproject.toml

@@ -21,3 +21,66 @@ testpaths = ["."]
 [build-system]
 requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"
+
+[tool.ruff]
+# Exclude a variety of commonly ignored directories.
+exclude = [
+    ".bzr",
+    ".direnv",
+    ".eggs",
+    ".git",
+    ".git-rewrite",
+    ".hg",
+    ".ipynb_checkpoints",
+    ".mypy_cache",
+    ".nox",
+    ".pants.d",
+    ".pyenv",
+    ".pytest_cache",
+    ".pytype",
+    ".ruff_cache",
+    ".svn",
+    ".tox",
+    ".venv",
+    ".vscode",
+    "__pypackages__",
+    "_build",
+    "buck-out",
+    "build",
+    "dist",
+    "node_modules",
+    "site-packages",
+    "venv",
+]
+
+# Same as Black.
+line-length = 88
+indent-width = 4
+
+# Assume Python 3.9
+target-version = "py39"
+
+[tool.ruff.lint]
+# Enable Pyflakes (`F`) and a subset of the pycodestyle (`E`)  codes by default.
+select = ["E4", "E7", "E9", "F"]
+ignore = []
+
+# Allow fix for all enabled rules (when `--fix`) is provided.
+fixable = ["ALL"]
+unfixable = []
+
+# Allow unused variables when underscore-prefixed.
+dummy-variable-rgx = "^(_+|(_+[a-zA-Z0-9_]*[a-zA-Z0-9]+?))$"
+
+[tool.ruff.format]
+# Like Black, use double quotes for strings.
+quote-style = "double"
+
+# Like Black, indent with spaces, rather than tabs.
+indent-style = "space"
+
+# Like Black, respect magic trailing commas.
+skip-magic-trailing-comma = false
+
+# Like Black, automatically detect the appropriate line ending.
+line-ending = "auto"