fix: only read each config file once on startup

tests/test_conf.py

@@ -109,6 +109,39 @@ baz = B
         self.assertIsNone(config.get('foo.bar'))
         self.assertEqual(config.get('foo.baz'), 'B')
 
+    def test_files_only_read_once(self):
+        base = self.write_file('base.conf', """
+[foo]
+bar = 1
+baz = A
+""")
+
+        middle = self.write_file('middle.conf', """
+[wutta.config]
+require = %(here)s/base.conf
+
+[foo]
+baz = B
+""")
+
+        top = self.write_file('top.conf', """
+[wutta.config]
+require = %(here)s/middle.conf
+
+[foo]
+baz = C
+""")
+
+        config = conf.WuttaConfig(files=[top, middle, base])
+        self.assertEqual(len(config.files_read), 3)
+        # nb. files_read listing is in order of "priority" which is
+        # same the as order in which files were initially read
+        self.assertEqual(config.files_read[0], top)
+        self.assertEqual(config.files_read[1], middle)
+        self.assertEqual(config.files_read[2], base)
+        self.assertEqual(config.get('foo.bar'), '1')
+        self.assertEqual(config.get('foo.baz'), 'C')
+
     def test_prioritized_files(self):
         first = self.write_file('first.conf', """\
 [foo]