consumer/producer: add interfaces

[bkeroackdsc]

To facilitate testing, I've found myself abstracting out the go-nsq API so I can swap in mock implementations.

nsq.Producer/nsq.Consumer should be interfaces so that users don't have to create their own abstraction layer.

[jehiah]

@bkeroackdsc While i use something similar (see gist) I'm not convinced that this belongs in the go-nsq library (or that it would be easy to do so w/o breaking api compatibility promises).

Perhaps we could add a nsqtesting subpackage?

thoughts @mreiferson ?

[mreiferson]

Yea, we couldn't return interfaces in the constructors without breaking compatibility, however we could introduce new interfaces that could provide a mechanism for speccing that out and being used in end-user tests?

[bkeroackdsc]

@mreiferson That seems like a reasonable compromise.

[sefasenturk95]

@mreiferson Are those new interfaces introduced already? I have to test a method that uses DeferredPublish..

[mreiferson]

No, PRs welcome!

[fairyhunter13]

Guys, I think you don't need to make those interfaces if you want. But, could you make a public API for change the connections instance in producer and consumer? I think the other way (alternative) to test this nsq is to implement custom net memory listener with a pipe. So, that we could implement a custom mock for the nsq.