public InMemoryFlagSource withStringFlag(FlagId flagId, String value) {
        return withRawFlag(flagId, new UnboundStringFlag(flagId, value).serializer().serialize(value));
    }
Basic in-memory flag source useful for testing

Creates an empty flag source that will make all flags return their default values (from {@code value()}).
The with* methods can be used to set a different return value.

@author freva
flags/src/main/java/com/yahoo/vespa/flags/InMemoryFlagSource.java