config: Add String config value and tests.

mopidy/utils/config.py

@@ -70,3 +70,13 @@ class ConfigValue(object):
         if self.secret:
             return '********'
         return self.serialize(value)
+
+
+class String(ConfigValue):
+    def deserialize(self, value):
+        value = value.strip()
+        validate_choice(value, self.choices)
+        return value
+
+    def serialize(self, value):
+        return value.strip()

tests/utils/config_test.py

@@ -86,3 +86,24 @@ class ConfigValueTest(unittest.TestCase):
     def test_format_masks_secrets(self):
         value = config.ConfigValue(secret=True)
         self.assertEqual('********', value.format(object()))
+
+
+class StringTest(unittest.TestCase):
+    def test_deserialize_strips_whitespace(self):
+        value = config.String()
+        self.assertEqual('foo', value.deserialize(' foo '))
+
+    def test_deserialize_enforces_choices(self):
+        value = config.String(choices=['foo', 'bar', 'baz'])
+
+        self.assertEqual('foo', value.deserialize('foo'))
+        with self.assertRaises(ValueError):
+            value.deserialize('foobar')
+
+    def test_serialize_strips_whitespace(self):
+        value = config.String()
+        self.assertEqual('foo', value.serialize(' foo '))
+
+    def test_format_masks_secrets(self):
+        value = config.String(secret=True)
+        self.assertEqual('********', value.format('s3cret'))