Unit test Android, getString from resource

I am trying to do an unit test for an android app and I need to get a string from res.string resources. The class that I want to test is a POJO class. I am doing the app in two languages, due to this, I need to get a string from resource. The problem is that I cannot get the context or the activity, is possible? I know that with Instrumentation test I can do it, but I need to test some functions (white box test) before to do the instrumentation test (black box test). This is the function that I have to test:

public void setDiaByText(String textView) {
    getll_diaSeleccionado().clear();
    if (textView.contains(context.getResources().getString(R.string.sInicialLunes))) {
        getll_diaSeleccionado().add(0);
        getIsSelectedArray()[0] = true;
        getI_idiaSeleccionado()[0] =1;

    } else
    {
        getIsSelectedArray()[0] = false;
        getI_idiaSeleccionado()[0] =0;
    }
}

And this is the test:

@Test
public void setDiaByTextView() {
    String texto = "L,M,X,J,V,S,D";

    alertaPOJO.setDiaByText(texto);

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

It crash when try to do context.getResources().getString(R.string.sInicialLunes))

If I put 'Mon' instead of context.getResources().getString(R.string.sInicialLunes)) or 'L' it work perfectly so, is possible to get the context or the activity in order to access to resource folder?

I am testing with Mockito and the setUp function is:

@Before
public void setUp() throws Exception {

    MockitoAnnotations.initMocks(this);
    mContext = Mockito.mock(Alerta.class);
    Mockito.when(mContext.getApplicationContext()).thenReturn(mContext);

    alertaPOJO = new AlertaPOJO();
}

Thanks

If you use MockK it's the same.

@RunWith(AndroidJUnit4::class)
class YourClassUnitTest : TestCase() {

    @MockK
    private lateinit var resources: Resources

    @Before
    public override fun setUp() {
        MockKAnnotations.init(this)
    }

    @Test
    fun test() {
        every {
            resources.getQuantityString(R.plurals.age, YEARS, YEARS)
        } returns AGE
        every {
            resources.getString(
                R.string.surname,
                SURNAME
            )
        } returns TITLE

        // Assume you test this method that returns data class 
        // (fields are calculated with getQuantityString and getString)
        val data = getData(YEARS, SURNAME)

        assertEquals(AGE, data.age)
        assertEquals(TITLE, data.title)
    }

    companion object {
        const val YEARS = 10
        const val AGE = "$YEARS years"
        const val SURNAME = "Johns"
        const val TITLE = "Mr. $SURNAME"
    }
}

See also Skip a parameter in MockK unit test, Kotlin to get a result of string resources for any data.