testsuite: add python unit tests for conf_builtin_get()

Problem: There are no unit tests for the Python interface to
flux_conf_builtin_get().

Add some very simple tests.

t/Makefile.am

@@ -288,6 +288,7 @@ TESTSCRIPTS = \
 	python/t0028-compat36.py \
 	python/t0029-fileref.py \
 	python/t0030-journal.py \
+	python/t0031-conf-builtin.py \
 	python/t1000-service-add-remove.py
 
 if HAVE_FLUX_SECURITY

t/python/t0031-conf-builtin.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+###############################################################
+# Copyright 2024 Lawrence Livermore National Security, LLC
+# (c.f. AUTHORS, NOTICE.LLNS, COPYING)
+#
+# This file is part of the Flux resource manager framework.
+# For details, see https://github.com/flux-framework.
+#
+# SPDX-License-Identifier: LGPL-3.0
+###############################################################
+
+import unittest
+
+import subflux  # noqa: F401
+from flux.conf_builtin import conf_builtin_get
+from pycotap import TAPTestRunner
+
+
+class TestConfBuiltin(unittest.TestCase):
+
+    def test_conf_builtin_get(self):
+        with self.assertRaises(ValueError):
+            conf_builtin_get("foo")
+
+        with self.assertRaises(ValueError):
+            conf_builtin_get("confdir", which="badarg")
+
+        self.assertIsNotNone(conf_builtin_get("confdir"))
+        self.assertIsNotNone(conf_builtin_get("confdir", which="intree"))
+        self.assertIsNotNone(conf_builtin_get("confdir", which="installed"))
+
+
+if __name__ == "__main__":
+    unittest.main(testRunner=TAPTestRunner())