use text_string() in a few places for io output

beetsplug/keyfinder.py

@@ -73,7 +73,7 @@ class KeyFinderPlugin(BeetsPlugin):
 
             key_raw = output.rsplit(None, 1)[-1]
             try:
-                key = key_raw.decode('utf8')
+                key = util.text_string(key_raw)
             except UnicodeDecodeError:
                 self._log.error(u'output is invalid UTF-8')
                 continue

test/helper.py

@@ -431,7 +431,7 @@ class TestHelper(object):
     def run_with_output(self, *args):
         with capture_stdout() as out:
             self.run_command(*args)
-        return out.getvalue().decode('utf-8')
+        return util.text_string(out.getvalue())
 
     # Safe file operations
 

test/test_ui.py

@@ -1013,7 +1013,7 @@ class ShowChangeTest(_common.TestCase):
             autotag.AlbumMatch(album_dist, info, mapping, set(), set()),
         )
         # FIXME decoding shouldn't be done here
-        return self.io.getoutput().lower().decode('utf8')
+        return util.text_string(self.io.getoutput().lower())
 
     def test_null_change(self):
         msg = self._show_change()