Testing

Constructor injection means most tests need no framework at all — you are calling a constructor:

val presenter = DefaultFirstPresenter(
    DefaultGreetingUseCase(FakeRepo()),
    SessionState(),
)

There is nothing to install, no test component to build, and no rule to apply. A fake is a class that implements the interface.

Unit tests never run the processor

Test compilations skip inference entirely: running it over test sources would generate a second registry that shadows the main graph. Your test sources can therefore hold as many throwaway implementations of an interface as they like without producing an ambiguity error in the app's graph.

Testing that the graph itself is correct

The graph is validated at build time, so "does it wire up" is answered by compiling, not by a test. What is worth a test is the behaviour of the classes in it — which is ordinary unit testing.

Instrumentation tests

For a test that runs against a real Application, Graph.start takes the same graph arguments it takes in production, so a test Application can pass fakes in:

class TestApp : Application() {
    override fun onCreate() {
        super.onCreate()
        Graph.start(this, apiKey = "test-key", timeoutMillis = 100)
    }
}

Anything you want to replace wholesale is a graph argument or an interface with a @Bind — both of which are decided in ordinary code you control per build type.