Injecting dependencies in multiprocess Android applications

Question

TLDR: I am developing an application which runs in multiple processes. For the purposes of UI testing, I want to inject a fake API dependency to make the app running under tests independent of network interactions, however, this doesn't seem to work in the multi-process setting.

I am using the approach described in this post, so I implemented a custom AndroidJUnitRunner which instantiates the application with mock dependencies (let it be MockApplication) instead of the one with real dependencies (let it be RealApplication). It does work and my app queries the fake API interface from the main process.

My app, however, uses multiple processes, e.g. there is a data processing Service which runs in its own process and which only starts on startService invocation from the application code. For some reason, this process runs with the instance of RealApplication, without any mock dependencies.

Is there any way I could make it work? I tried digging into Android code responsible for application instantiation, but haven't really found anything particular useful yet.

P.S. I am using Dagger 2 for DI, but this is probably not really relevant.

Answer 1

The problem is that your custom application class does not override real one in the AndroidManifest.xml.

You're just telling the instrumentation test runner to run your custom application class but then if app starts another process, Android Framework won't even know that it needs to run your custom application class instead of real one.

So, I'd suggest you to override the application class to the custom one in AndroidManifest.xml during the connectedAndroid task execution, as a result your app will use custom class even without hacking the test runner and whenever new processes start.

Answer 2

I struggled on this problem too as I need to mock network calls emitted from a Service started in its own process.

To use a custom Application object (MockApplication) in every process of your app during your tests, a solution is to inject a build variable in your AndroidManifest.xml with the help of manifestPlaceholders.

I defined two product flavors in build.gradle:

productFlavors {
    mock {
        manifestPlaceholders = [application:".MockApplication"]
    }
    prod {
        manifestPlaceholders = [application:".RealApplication"]
    }

}

• prod : will set the real Application object (RealApplication) in manifest
• mock : will set the mock Application object (MockApplication) to mock network calls

In AndroidManifest.xml, use the variable "application" like this:

<application 
    android:label="@string/app_name"
    android:name="${application}">

Now, when you want to use the MockApplication, just run your instrumentation test with build variant "mockDebug"