testing: exceptions silently ignored in EventBus subscribtions

[jpommerening]

I was testing the following code:

debugEventBus.subscribe( `didLoad.page.${instance}`, ( { [ type ]: ref } ) => {
   console.info( ... ); // added this line because was not 100% sure this was called w/ karma
   log.debug( ... ); // added this line earlier to get some feedback in my browser
   pages.push( ref );
   console.info( ... );  // had to add this to notice that "log" was undefined
} );

So, sure enough, I forgot to pass the log instance in my test setup. However, shouldn't we log something when subscribers throw?

[x1B]

Since eventBus.create accepts an error-handler function as the last argument, the mock event bus should probably always configure a "loud" error handler.

Regarding general log-behaviour in tests I am on the fence:

• On on hand, I like to be able to test behavior that causes log.error on purpose without being confused by red/yellow messages in terminal or browser console.
• On the other hand, "mute by default" makes diagnosing actual problems much harder.

Possible solution:

• allow to setup mock log "expectations" that will then be silently dropped, while all other logging goes through.
• users could also be able to require no unexpected logging, turning any additional log message (above the specified level) into a test failure.

[jpommerening]

@x1B so the mock event bus currently does log the error, it's just not appearing because of the test infrastructure?
I'm not having an issue with logging in general; couldn't we just re-throw the error (or a new one with the message constructed by the event bus) when testing?
I don't think there is a legitimate use case for testing throwing subscribers. IMO subscriptions that throw should always cause tests to fail.

[x1B]

@jpommerening agreed, let's make it so (tm)

[x1B]

Just for completeness: this is not a problem in widget tests (or we would've noticed this far sooner), because laxar-mocks passes a jasmine-aware error handler to the mock event bus:

https://github.com/LaxarJS/laxar-mocks/blob/fa85b6b/laxar-mocks.js#L238

[x1B]

Implemented on master (v2.0.0).