ci: run the unit tests when any workflow or action they cover changes

test-freebsd.yml is the only workflow that runs tests/, but its path filter
still lists the FreeBSD-era files. A change to sonarcloud.yml,
supply-chain.yml, nix.yml, ast-grep.yml, or to actions such as arch-package,
resolve-version, ast-grep or checkout-craft-fonts ran none of their tests:
#86 (sonarcloud.yml and the README) and #90 (sonarcloud.yml) merged without
test_sonarcloud.py running. Match every workflow, action and test file, and
test that the filter does, with GitHub's glob rules.

.github/workflows/test-freebsd.yml

@@ -1,28 +1,17 @@
 name: Shared FreeBSD workflow tests
 
+# The suite covers every workflow and action, not only FreeBSD, so a change to any of them runs it.
 on:
   pull_request:
     paths:
-      - .github/workflows/freebsd.yml
-      - .github/workflows/release.yml
-      - .github/workflows/gate.yml
-      - actions/freebsd-cargo-cache/**
-      - actions/checkout-craft-i18n/**
-      - .github/workflows/windows-arm64.yml
-      - .github/workflows/test-freebsd.yml
-      - actions/install-apt-packages/**
+      - .github/workflows/**
+      - actions/**
       - tests/**
   push:
     branches: [main]
     paths:
-      - .github/workflows/freebsd.yml
-      - .github/workflows/release.yml
-      - .github/workflows/gate.yml
-      - actions/freebsd-cargo-cache/**
-      - actions/checkout-craft-i18n/**
-      - .github/workflows/windows-arm64.yml
-      - .github/workflows/test-freebsd.yml
-      - actions/install-apt-packages/**
+      - .github/workflows/**
+      - actions/**
       - tests/**
   workflow_dispatch:
 

tests/test_unit_test_triggers.py

@@ -0,0 +1,41 @@
+"""The workflow that runs these tests must start for a change to anything they test."""
+
+from pathlib import Path
+import re
+import unittest
+
+import yaml
+
+
+ROOT = Path(__file__).resolve().parents[1]
+WORKFLOW = yaml.load((ROOT / ".github/workflows/test-freebsd.yml").read_text(), Loader=yaml.BaseLoader)
+
+
+def matches(path, pattern):
+    # GitHub path filters: * stops at /, ** crosses it.
+    regex = "".join(".*" if part == "**" else "[^/]*" if part == "*" else re.escape(part)
+                    for part in re.split(r"(\*\*|\*)", pattern))
+    return re.fullmatch(regex, path) is not None
+
+
+class UnitTestTriggerTests(unittest.TestCase):
+    def test_every_workflow_action_and_test_file_triggers_the_tests(self):
+        files = [path.relative_to(ROOT).as_posix()
+                 for directory in (".github/workflows", "actions", "tests")
+                 for path in (ROOT / directory).rglob("*")
+                 if path.is_file() and "__pycache__" not in path.parts]
+        self.assertIn(".github/workflows/sonarcloud.yml", files)
+        for event in ("pull_request", "push"):
+            patterns = WORKFLOW["on"][event]["paths"]
+            for file in files:
+                with self.subTest(event=event, file=file):
+                    self.assertTrue(any(matches(file, pattern) for pattern in patterns))
+
+    def test_matches_follows_github_globs(self):
+        self.assertTrue(matches("actions/ast-grep/action.yml", "actions/**"))
+        self.assertFalse(matches("actions/ast-grep/action.yml", "actions/*"))
+        self.assertTrue(matches(".github/workflows/nix.yml", ".github/workflows/*.yml"))
+
+
+if __name__ == "__main__":
+    unittest.main()