Write/create file within Android Instrumentation context

Question

I have a class that creates (or opens) a file to write some data to it. This class receives a Context in the constructor, saves it in an instance field, and then uses it to call the context.openFileOutput method.

When running the application, I instantiate this class by passing the ApplicationContext as the Context, and everything is working as expected.

However, when I try to test this class with an Instrumentation Test, I get a NullPointerException. I'm passing the getInstrumentation().getContext() context, which I know corresponds to the context of the test, and not the one of the real app.

getInstrumentation().getContext().openFileOutput("myFile", Context.MODE_PRIVATE); // This throws NullPointerException :( :(

Within the test, I need this file to be created in the test package and not in the app package, as I don't want overwrite the file in my app.

I know there is a RenamingDelegatingContext class out there, but I cannot pass this context to my class since my class also opens a raw resource, and I want that resource to be different when running the test (something like a mocked resource).

I searched a lot about this, and there is no documentation about the Instrumentation Context. I couldn't find its limitations nor anything that solves my problem.

Do you know how to tackle this?

Answer 1

I can't recall when this was changed, but the current method to get a Context object during Instrumented testing is to import

import android.support.test.InstrumentationRegistry;

and call

InstrumentationRegistry.getContext();

Hope this helps!