Add a test that verifies ruff, black, and mypy all pass

This fels good!

Topic: clean_rewrite

test/linter_test.py

@@ -0,0 +1,24 @@
+from pathlib import Path
+import subprocess
+
+from .test_case import TestCase
+
+
+class LinterTest(TestCase):
+    """
+    Test that ruff, black, and mypy run cleanly.
+    """
+
+    HOME = Path(__file__).parent.parent
+
+    def test_ruff(self) -> None:
+        code = subprocess.check_call(["ruff", str(self.HOME)])
+        self.assertEqual(code, 0)
+
+    def test_black(self) -> None:
+        code = subprocess.check_call(["black", "--check", str(self.HOME)])
+        self.assertEqual(code, 0)
+
+    def test_mypy(self) -> None:
+        code = subprocess.check_call(["mypy", str(self.HOME)])
+        self.assertEqual(code, 0)