How does exactly custom Shadow objects work in Robolectric?

Question

If I write a custom Shadow for my Activity, and registering it with RobolectricTestRunner, will the framework intercept the Activity with my custom Shadow whenever it's started?

Thanks.

Answer 1

The short answer is no.

Robolectric is selective about what classes it intercepts and instruments. At the time of this writing, the only classes that will be instrumented must have a fully qualified classname match one of these selectors:

android.* 
com.google.android.maps.* 
org.apache.http.impl.client.DefaultRequestDirector

The whole reason for Robolectric's existence is that the classes provided in the Android SDK jar throw exceptions when invoked in a JVM (i.e. not on an emulator or device). Your application's Activity has source that is not 'hostile' (it probably does not throw exceptions when the methods or constructors are invoked). Robolectric's intended purpose is to allow you to put your application's code under test, which would otherwise not be possible due to the way the SDK is written. Some of the other reasons why Robolectric was created were:

• The SDK does not always have methods that would allow you to query the state of the Android objects manipulated by your application's code. Shadows can be written to provide access to this state.
• Many of the classes and methods in the Android SDK are final and/or private or protected, making it difficult to create the dependencies needed by your application code that would otherwise be available to your application code.

The code could clearly be changed to shadow any class. There has been talk in the past about extracting the shadowing features into a standalone library, to assist writing tests using some other test-hostile api.

Why do you want to shadow your Activity?