fix(post-install): updating optimizations of both flows prints only its steps

.github/scripts/tests/test_install_functions_sourced_twice.py

@@ -0,0 +1,39 @@
+"""The shared install functions are sourced by both post-install flows. An
+update that runs functions of the two sources the file twice in one shell,
+which has to be as quiet as the first time."""
+
+from pathlib import Path
+import shutil
+import subprocess
+import unittest
+
+ROOT = Path(__file__).resolve().parents[3]
+SHARED = ROOT / "scripts/global/utils-install-functions.sh"
+
+
+@unittest.skipUnless(shutil.which("bash"), "bash is needed")
+class SourcedTwiceTests(unittest.TestCase):
+    def source(self, times):
+        script = "; ".join([f'source "{SHARED}"'] * times) + '; echo "${PMX_NIC_LINK_DIR}|${#PMX_DKMS_COMPONENTS[@]}"'
+        return subprocess.run(["bash", "-c", script], capture_output=True, text=True, check=False)
+
+    def test_a_second_source_prints_nothing(self):
+        once, twice = self.source(1), self.source(2)
+        self.assertEqual(twice.stderr, once.stderr)
+        self.assertNotIn("readonly variable", twice.stderr)
+        self.assertEqual(twice.returncode, 0)
+
+    def test_the_values_are_the_same_and_stay_read_only(self):
+        self.assertEqual(self.source(2).stdout.strip(), "/etc/systemd/network|2")
+        attempt = subprocess.run(["bash", "-c", f'source "{SHARED}"; PMX_NIC_LINK_DIR=/tmp'],
+                                 capture_output=True, text=True, check=False)
+        self.assertIn("readonly variable", attempt.stderr)
+
+    def test_no_other_shared_file_declares_a_read_only_variable_unguarded(self):
+        for path in sorted((ROOT / "scripts/global").glob("*.sh")) + [ROOT / "scripts/utils.sh"]:
+            for line in path.read_text(errors="replace").splitlines():
+                self.assertFalse(line.startswith(("readonly ", "declare -r ")), f"{path.name}: {line[:60]}")
+
+
+if __name__ == "__main__":
+    unittest.main()