diff --git a/tests/test-ui-config.out b/tests/test-ui-config.out
--- a/tests/test-ui-config.out
+++ b/tests/test-ui-config.out
@@ -1,5 +1,7 @@
 [('bool1', 'true'), ('bool2', 'false'), ('string', 'string value')]
 [('list1', 'foo'), ('list2', 'foo bar baz'), ('list3', 'alice, bob'), ('list4', 'foo bar baz alice, bob')]
+Error in configuration section [interpolation]:
+'%' must be followed by '%' or '(', found: '%bad2'
 ---
 'string value'
 'true'
@@ -27,3 +29,17 @@ True
 ['foo bar']
 ['foo', 'bar']
 ---
+'hallo'
+'hallo world'
+Error in configuration section [interpolation] parameter 'value3':
+Bad value substitution:
+	section: [interpolation]
+	option : value3
+	key    : novalue
+	rawval : 
+
+Error in configuration section [interpolation] parameter 'value4':
+bad interpolation variable reference '%(bad)1'
+Error in configuration section [interpolation] parameter 'value5':
+'%' must be followed by '%' or '(', found: '%bad2'
+---