This is how one can use parameterized tests along with Mockito to provide cyclic tests of Event Handlers

VfxSetUserTest.java

package com.gdetotut.login;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.mockito.ArgumentCaptor;

import java.util.Arrays;
import java.util.Collection;

import static org.junit.Assert.assertEquals;
import static org.mockito.ArgumentMatchers.eq;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;

/**
 * This is cyclic test with parameters. So we use parameterized concept.
 */
@RunWith(Parameterized.class)
public class VfxSetUserTest {

    private int index;

    private VfxUser.State state;

    public VfxSetUserTest(int index, VfxUser.State state) {
        this.index = index;
        this.state = state;
    }

    // {name} is optional just for the logging output.
    @Parameterized.Parameters(name = "{index}: param = {0}, res = {1}")
    public static Collection getParameters() {
        return Arrays.asList(new Object[][]{
                {0, VfxUser.State.US_GodMode},
                {1, VfxUser.State.US_Disp},
                {2, VfxUser.State.US_Admin},
                {3, VfxUser.State.US_NotReg},
                {10, VfxUser.State.US_NotReg},
                {-1, VfxUser.State.US_NotReg}
        });
    }

    /**
     * We set various parameter for {@link VfxModel#setUser} and await parameterized result.
     */
    @Test
    public void testModel() {
        VfxModel service = VfxModel.INSTANCE;
        VfxModel.OnEventListener event = mock(VfxModel.OnEventListener.class);
        service.setListener(event);

        service.setUser(index);
        ArgumentCaptor<VfxUser> captor = ArgumentCaptor.forClass(VfxUser.class);
        verify(event).onUserChanged(captor.capture(), eq(""));
        VfxUser captured = captor.getValue();
        assertEquals(state, captured.getState());
    }



}