HomeViewModel.java

package com.sunilsahoo.sonarqube.validator;

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MediatorLiveData;
import androidx.lifecycle.ViewModel;

public class HomeViewModel extends ViewModel {
    private MediatorLiveData<String> liveData = new MediatorLiveData<>();

    public LiveData<String> getLiveData() {
        return liveData;
    }

    public void execute() {
        liveData.postValue("Loading");
        //perform other operation
        liveData.postValue("Success");
    }
}

HomeViewModelTest.java

package com.sunilsahoo.sonarqube.validator;

import androidx.lifecycle.MediatorLiveData;

import org.junit.Before;
import org.junit.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

import static org.mockito.BDDMockito.then;
import static org.mockito.BDDMockito.willDoNothing;
import static org.mockito.BDDMockito.willReturn;
import static org.mockito.Mockito.anyString;
import static org.mockito.Mockito.spy;
import static org.mockito.Mockito.times;

public class HomeViewModelTest {
    @Mock
    private MediatorLiveData<String> liveData;
    @InjectMocks
    private HomeViewModel homeViewModel;

    @Before
    public void setUp() {
        MockitoAnnotations.initMocks(this);
        homeViewModel = spy(homeViewModel);
        willReturn(liveData).given(homeViewModel).getLiveData();
        willDoNothing().given(liveData).postValue(anyString());
    }

    @Test
    public void testExecute() throws Exception {
        homeViewModel.execute();
        then(liveData).should(times(1)).postValue("Loading");
        then(liveData).should(times(1)).postValue("Success");
    }
}