Inherit mock state

[pepicrft]

I recently came across this blog post, and made me think that it'd be useful if Mimic had another mode besides private or global, inherited, such that processes could inherit the mock configuration scoped to a particular test using something like ProcessTree.

We love :mimic, and we'd love to continue using it, but having to mark some of our tests as async: false because explicitly allowing access to mocks is not possible is a bit annoying.

[edgurgel]

@pepicrft I like the idea, but I feel like private sort of already does a little bit of that as you can see here (if I understood the issue ofc).

I would be happy to change this to rely on ProcessTree.known_ancestors(pid) for private.

[pepicrft]

That was quick :).
In think I misunderstood how private works, so I don't think any changes are necessary.

Giving it another thought, I think what I need is a bit out of the scope of Mimic. For example, I have tests that transitively depend on a "cache" process that's started with the app, and I'd like to swap that process with another one. One solution is using Mimic to sub its interface, but in some cases where I do integration tests, I'd like to tell some piece of logic deep in the process tree: "use this other instance". So what I need of more of a solution to propagate a value down the tree such that I don't have to pass the value through opts (e.g. [cache: test_cache])

test "unit test" do
   stub(Cache, :get, fn "key" -> "value" end)

   subject()
end

test "integration test" do
   {:ok, cache} = Cache.start_link()
   subject(cache: cache) #I'm currently doing
   subject() # But I'd like to do just
end

[edgurgel]

Hmm I'm not sure this is out of scope.

Mimic won't impact your integration tests if it's not being called explicitly. It should just use your Cache nicely if I understood your example.

test "unit test" do
   # How will `subject` call Cache ? Is it from another process? If so you might need to call Mimic.allow with the pid of that process
   stub(Cache, :get, fn "key" -> "value" end)

   subject()
end

test "integration test" do
  # How will subject find this Cache? Through a named process? If so this should just work I think? 
   {:ok, cache} = Cache.start_link()
   subject() # But I'd like to do just
end

If you could get a minimal example we can find out if Mimic suits your or not as of now I'm mostly guessing what Cache does and how it's called 🤔

[pepicrft]

Cache is a running process in the application tree registered with a given name. The approach I'm taking with the tests, depending on caching, is swapping that instance with one scoped to the test, instead of stubbing the interface of Cache (more of an integration test). So I want to know the best pattern to tell the subject under the test: don't use the default process registered with name X, but use this other one. The approach I'm currently taking is passing it as an option, but that means I have to go to the deepest, most critical piece of business logic that accesses the cache. Since Mimic has to do something similar for mocks, keeping a registry that binds a particular mock to a test process, I would like to leverage this for a similar form of dependency injection. In other words, some API where I can say: "If someone wants to access process X, use Y".