Android Instrumentation Tests

We are currently working on an Android App in collaboration with the guys from Hochzeitsportal24. Yes, it’s a wedding planner ;)

Anyway, since we use Maven for all our Java projects, we also went with it for this project. I had some experience with the android-maven-plugin because I used it with two of my prior Android Apps.

Our app setup consists of an android app module and an instrumentation test module. Besides these two modules, we have a third module that we call the core module. It contains only android independent code and unit tests for this code. This setup works great with maven on the command line and on the Jenkins build server, however there are some issues if you use it in Eclipse.

Here the m2e plugin handles the build path of your projects and this leads to a problem where the classes from the core module get included in the instrumentation test APK. As a result of this you cannot launch the instrumentation tests from Eclipse because the test runner fails with an exception like this:

java.lang.IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation

Prior to this exception you can see several ClassNotFoundExceptions which make you believe that you are missing some jar libraries in your class path. However, this is a totally wrong direction.

The true problem here is the last exception. It tells you that you have two instances of the same class in your test scenario. This happens when one version is in your app APK and a second version is in the test APK. To verify this you can use the dex2jar tool and convert the classes.dex file to a jar file and then check the contents of this file.

This happens in our setup due to the fact that we need the classes from the core module in our app and in the instrumentation tests. Since all modules are under a heavy development we use SNAPSHOT dependencies. And now m2e kicks in and resolves the SNAPSHOT dependencies into project dependencies. This way the classes from the core module appear in the test module and get added to the test APK. I’ve tried several solutions and actually none of them really works in the long term. I’ll document them here so you might choose one that hurts you less.

1. Declare the core module dependency with scope “provided” in the test module pom.xml. This works from the command line but not in Eclipse since m2e resolves the SNAPSHOT dependency anyway.
2. Declare the core module as optional in the app module pom.xml. This actually works in Eclipse but it fails on the command line because here the compiler cannot find the classes.
3. Uncheck the “Maven Dependencies” from the “Order and Export” tab in Java build path config. This solves the problem in Eclipse but only until the next time you hit Maven/Update Project…

Right now I’m using the third option since it is somehow predictable and we rely on a clean build on the Jenkins server. One possible long term solution might be to look into the Android Maven Plugin and change it in a way where it hides the “provided” dependencies from m2e.