verify(messageSource, times(1)).getMessage(fragResult, new Object[]{}, Locale.CANADA_FRENCH);
// exercise the optional args passing:
when(frag.execute()).thenReturn(fragResultWithArgs);
lambda.execute(frag, out);
verify(messageSource, times(1)).getMessage(fragResult, new Object[]{"foo", "baz", "burp"}, Locale.CANADA_FRENCH);
verifyNoMoreInteractions(messageSource);