CI migration: interop-jdc-change-upstream MG to Integration Test

[plebhash]

as part of #1121 a good first MG test to migrate is interop-jdc-change-upstream because:

• it covers many roles (including JD)
• it requires the usage of a mock, which we still don't have in the integration test framework

this will help us continue shaping up the integration test framework, as a continuation of #1122

[plebhash]

to elaborate a bit more on the requirement of a mock:

this test is essentially making sure that JDC has a sane implementation for the fallback mechanism, which is one of the major selling points of JD:

assuming a JDS+Pool have already acknowledged some specific job, Pool rejecting shares must trigger JDC to switch upstreams

now, how do we get a Pool to reject shares that are supposed to be valid? it wouldn't really make sense to add that kind of functionality to SRI Pool implementation, which is supposed to be sane

therefore, we need a way to mock a role by having something that establishes a connection and sends custom messages

[plebhash]

I did some experimentation where I tried modifying the Sniffer struct to give it the ability to inject messages, but this modification proved not to be trivial

I wonder if an easier approach could consist of the following:

we add a new Mock struct that does not relay messages... in fact, it doesn't even need to have both upstream+downstream connections, as one single connection would suffice

Mock would keep a queue record with all messages it receives form its single connection, and allow the user to assert against them (much like Sniffer)

but it would also have a method that would allow the user to inject some custom message into the connection

[jbesraa]

I did some experimentation where I tried modifying the Sniffer struct to give it the ability to inject messages, but this modification proved not to be trivial

I wonder if an easier approach could consist of the following:

we add a new Mock struct that does not relay messages... in fact, it doesn't even need to have both upstream+downstream connections, as one single connection would suffice

Mock would keep a queue record with all messages it receives form its single connection, and allow the user to assert against them (much like Sniffer)

but it would also have a method that would allow the user to inject some custom message into the connection

Yea I also think it need to be something a bit different than the Sniffer. It would need to be a "role" that can act as either upstream or downstream. As mentioned, we would also need to define some functionality to tell it "when you receive message X return message Y".
This issue requires also a bit of work in the testing framework setup, allowing us to start JDS and JDC in test env. As we already done #1095 and #993, this should not be a huge deal.

Anyway, please assign me here as I already started looking into this.

[jbesraa]

OK, I take back my previous comment. It ended up being more straightforward to implement in the Sniffer than I initially thought. There is a draft here 961caa7.

[plebhash]

currently blocked by #1245