AssertionFailedError in ApplicationTestCase.createApplication() in newer Android versions when using MockContext

Question

I am writing an Android ApplicationTestCase (TemperatureConverterApplicationTests example found in Android Application Testing Guide by Diego T. Milano on page 171). Th

Answer 1

The Instrumentation.newApplication() method will return an Application object. You are trying to cast it to whatever T is. If T is not a super class or sub class of Application you will get a ClassCastException. In Java you can only cast an object to something that is a super class or sub class of that object. If it isn't then the exception will be thrown.

FOR EXAMPLE:

Object x = new Integer(0);
System.out.println((String)x);

This will throw a ClassCastException on the second line because your trying to cast x (an Integer object) to a String. Because a String and Integer are not sub or super classes of each other.

Answer 2

I get this behaviour too. I've worked around it by extending ContextWrapper:

public class RenamingMockContext extends RenamingDelegatingContext
{
    private static final String PREFIX = "test.";

    public RenamingMockContext(Context context)
    {
        super(new ContextWrapper(context), PREFIX);
    }

    @Override
    public String getPackageName()
    {
        return PREFIX + super.getPackageName();
    }
}