Can not test Timer with processing time domain

I have a stateful DoFn which has a timer on PROCESSING_TIME domain. While writing tests, I noticed that it does not react to `advanceProcessingTime()` on tests stream. Problem seems to be here:

https://github.com/apache/beam/blob/master/runners/core-java/src/main/java/org/apache/beam/runners/core/SimpleDoFnRunner.java#L260

I can only tell that patching this place works for direct runner tests. Not sure about broader impact on other runners since it is in `runner-core`