test: the installer library's shell tests run with the suite

conf/test_install_lib.sh tested conf/install-lib.sh, but no CI step or
test ran it. It moves to webvirtcloud/tests/sh/install_lib.test.sh, takes
the library's path as its argument, and test_install_lib runs it in bash,
as the JS tests run in node.

conf/install-lib.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 # Idempotent installer primitives. Sourcing this file has NO side effects;
-# it only defines functions, so it can be unit-tested (conf/test_install_lib.sh).
+# it only defines functions, so it can be unit-tested (webvirtcloud/tests/sh/install_lib.test.sh).
 
 # Create <data_dir>/secret_key (mode 600) only if missing or empty; keep an
 # existing key. A blank key would make Django fail to boot, so an empty file is

webvirtcloud/tests/sh/install_lib.test.sh

@@ -1,9 +1,9 @@
 #!/usr/bin/env bash
-# Unit tests for conf/install-lib.sh. Run: bash conf/test_install_lib.sh
+# Unit tests for conf/install-lib.sh, run by webvirtcloud/tests/test_install_lib.py:
+# bash webvirtcloud/tests/sh/install_lib.test.sh conf/install-lib.sh
 set -u
-here="$(cd "$(dirname "$0")" && pwd)"
 # shellcheck source=/dev/null
-. "$here/install-lib.sh"
+. "$1"
 
 fail=0
 check() { if eval "$2"; then echo "ok - $1"; else echo "NOT ok - $1"; fail=1; fi; }

webvirtcloud/tests/test_install_lib.py

@@ -0,0 +1,20 @@
+"""The installer's functions (conf/install-lib.sh), tested in bash."""
+
+import shutil
+import subprocess
+import unittest
+from pathlib import Path
+
+from django.conf import settings
+
+BASE = Path(settings.BASE_DIR)
+
+
+class InstallLibTestCase(unittest.TestCase):
+    @unittest.skipUnless(shutil.which("bash"), "bash is not installed")
+    def test_install_lib(self):
+        result = subprocess.run(
+            ["bash", str(BASE / "webvirtcloud/tests/sh/install_lib.test.sh"), str(BASE / "conf/install-lib.sh")],
+            capture_output=True, text=True, timeout=120,
+        )
+        self.assertEqual(result.returncode, 0, result.stdout + result.stderr)