What’s the difference between getTargetContext() and getContext (on InstrumentationRegistry)?

InstrumentationRegistry is an exposed registry
instance that holds a reference to the instrumentation running in the
process and it’s arguments and allows injection of the following
instances:

• InstrumentationRegistry.getInstrumentation(), returns the
  Instrumentation currently running.
• InstrumentationRegistry.getContext(), returns the Context of this
  Instrumentation’s package.
• InstrumentationRegistry.getTargetContext(),
  returns the application Context of the target application.
• InstrumentationRegistry.getArguments(), returns a copy of arguments
  Bundle that was passed to this Instrumentation. This is useful when
  you want to access the command line arguments passed to
  Instrumentation for your test.

EDIT:

So when to use getContext() vs getTargetContext()?

The documentation doesn’t do a great job of explaining the differences so here it is from my POV:

You know that when you do instrumentation tests on Android then you have two apps:

1. The test app, that executes your test logic and tests your “real” app
2. The “real” app (that your users will see)

So when you are writing your tests and you want to load a resource of your real app, use getTargetContext().

If you want to use a resource of your test app (e.g. a test input for one of your tests) then call getContext().