Add Unit test for fetching DisplayName

import org.robolectric.RobolectricTestRunner;

import org.robolectric.annotation.Config;

import java.io.IOException;

import java.util.Map;

import io.reactivex.Observable;

import it.niedermann.owncloud.notes.persistence.sync.OcsAPI;

import it.niedermann.owncloud.notes.shared.model.Capabilities;

import it.niedermann.owncloud.notes.shared.model.OcsResponse;

import it.niedermann.owncloud.notes.shared.model.OcsUser;

import okhttp3.Request;

import retrofit2.Call;

import retrofit2.Callback;

import retrofit2.Response;

import static org.junit.Assert.assertEquals;

import static org.mockito.ArgumentMatchers.any;

        assertEquals("[1.0]", capabilities.getApiVersion());

        assertEquals("ETag should be read correctly from response but wasn't.", "1234", capabilities.getETag());

    }

    @SuppressWarnings("unchecked")

    @Test

    public void testGetDisplayName() throws IOException {

        final OcsResponse<OcsUser> mockOcs = new OcsResponse<>();

        mockOcs.ocs = new OcsResponse.OcsWrapper<>();

        mockOcs.ocs.data = new OcsUser();

        mockOcs.ocs.data.displayName = "Peter";

        final Response<OcsResponse<OcsUser>> ocsUserResponseMock = Response.success(mockOcs);

        final Call<OcsResponse<OcsUser>> callMock = mock(Call.class);

        when(callMock.execute()).thenReturn(ocsUserResponseMock);

        when(ocsAPI.getUser(any())).thenReturn(callMock);

        final String user = CapabilitiesClient.getDisplayName(ApplicationProvider.getApplicationContext(), ssoAccount, apiProvider);

        assertEquals("Peter", user);

    }

}

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