Unit test Android, getString from resource

Untested: would it work to use the below, and probably targetContext?

android {
   testOptions {
     unitTests {
        includeAndroidResources = true
     }
  }
}

If you are using Context only for obtaining String resource, I would go by mocking only getResources().getString() part like this (see JUnit4 notation):

@RunWith(MockitoJUnitRunner.class)
public class AlertaPOJOTest {

  @Mock
  Context mMockContext;

  @Test
  public void setDiaByTextView() {
     String texto = "L,M,X,J,V,S,D";
     when(mMockContext.getString(R.string.sInicialLunes))
       .thenReturn(INITIAL_LUNES);


     alertaPOJO.setDiaByText(texto);

     assertEquals(alertaPOJO.getIsSelectedArray()[0], true);
     assertEquals(alertaPOJO.getI_idiaSeleccionado()[0], 1);
   } 
}

There are many reasons to stay with JVM tests, most important one, they are running quicker.