How to unit test serial ports in Java on Android

Question

I'm aware that Android does not provide out-of-the-box access to the serial ports unless the device is rooted or a custom Android version is flashed, say on a BeagleBone Black board -- which is exactly my case. Using the Android SerialPort API project I am able to access and test the serial ports of my device through the sample GUI app (slightly modified).

However, I'd like to also add JUnit tests for the Serial API because I will be expanding it into a library module for client programmers to use. I tried using AndroidTestCase, but I'm receiving the error:

java.lang.UnsatisfiedLinkError: Native method not found:  
com.XXX.android.serialport_api.SerialPort.open:  
(Ljava/lang/String;II)Ljava/io/FileDescriptor;
at com.XXX.android.serialport_api.SerialPort.open(Native 
Method)
at com.XXX.android.serialport_api.SerialPort.<init    
(SerialPort.java:32)

It seems to me the serialport.so files are not loaded/visible inside the mock environment provided by AndroidTestCase. I'm using the standard test structure created by the "New Module" wizard in Android Studio.

Any advice or hint would be appreciated because my search on the topic turned nothing out. I'll be happy to provide test class and implementation if needed (although the implementation is pretty much the same as the SerialPort.java class in the open source sample referenced above).

Muscid

"It seems to me the serialport.so files are not loaded/visible inside the mock environment provided by AndroidTestCase" -- AndroidTestCase is not using a mock environment, at least in terms of how the work "mock" is usually used in Android testing. Where/how are you integrating serialport.so into your project? – Cilice

I'm integrating the .so's by dropping the libs in the src/main/jniLibs of the main project in Android Studio. No change to the Gradle files. The build system seems to find and include them automatically. Both the sample deployed .apk as well as the test .apk include the .so libs. One thing to note, though is that the open source sample app builds to 2.5MB .dex file in the .apk, whereas the .dex file in my test .apk is about 8K. – Muscid

Look for the answer below. – Muscid

Answer 1

I found the issue. The package name is hardcoded in the pre-compiled .so files. So instead of using a custom package name like com.XXX.XXX one has to put the SerialPort (and other implementing classes) in a top-level package directly under the /java folder. The package name should be exactly android_serialport_api -- just like in the library sample.

Muscid

You are the boss, thank you! Without your comment I would be stuck forever with this:) – Lepine