Согласно документации Instrumentation.class. Там написано
* Return the Context of this instrumentation's package. Note that this is
* often different than the Context of the application being
* instrumentated, since the instrumentation code often lives is a
* different package than that of the application it is running against.
* See {@link #getTargetContext} to retrieve a Context for the target
* application.
*
* @return The instrumentation's package context.
*
* @see #getTargetContext
Итак, вы используете неверный контекст для вашего случая. Вам нужен контекст устройства, который вы можете получить следующим образом.
mContext = InstrumentationRegistry.getInstrumentation().getContext();
И, согласно документации, это дает вам контекст вашего приложения на вашем устройстве.
* Return a Context for the target application being instrumented. Note
* that this is often different than the Context of the instrumentation
* code, since the instrumentation code often lives is a different package
* than that of the application it is running against. See
* {@link #getContext} to retrieve a Context for the instrumentation code.
*
* @return A Context in the target application.