Example Android Unit Test,

LaunchActivityTest.java

package com.example.android.testingfun;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.ArgumentCaptor;
import org.mockito.Mock;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

import static org.mockito.Matchers.any;
import static org.mockito.Matchers.anyInt;
import static org.mockito.Mockito.doNothing;
import static org.mockito.Mockito.doReturn;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.spy;
import static org.mockito.Mockito.verify;
import static org.powermock.api.support.membermodification.MemberMatcher.method;
import static org.powermock.api.support.membermodification.MemberModifier.suppress;

/**
 * Tests LaunchActivity in isolation from the system.
 */
@RunWith(PowerMockRunner.class)
@PrepareForTest(LaunchActivity.class)
public class LaunchActivityTest {

    private LaunchActivity tested;

    @Mock
    private Button mockButton;

    @Before
    public void setUp() throws Exception {
        // We will Spy our tested activity so that we will be able to give it some input when
        //  for example the FindViewByID method is called.
        tested = spy(LaunchActivity.class);
        doReturn(mockButton).when(tested).findViewById(anyInt());
        // We need to suppress methods from the Base Activity. This is why we need PowerMock, there
        //  are other ways but are more intrusive in our code.
        suppress(method(Activity.class, "onCreate", Bundle.class));
        suppress(method(Activity.class, "setContentView", int.class));
    }

    @Test
    public void shouldSetupListener() throws Exception {
        // When we call the onCreate...
        tested.onCreate(mock(Bundle.class));

        // Then the setOnClickListener method will be called.
        verify(mockButton).setOnClickListener((View.OnClickListener) any());
    }

    @Test
    public void shouldStartActivity() throws Exception {
        // Let's setup our mockButton so that it will capture the listener
        ArgumentCaptor<View.OnClickListener> captor =
                ArgumentCaptor.forClass(View.OnClickListener.class);
        doNothing().when(mockButton).setOnClickListener(captor.capture());

        // When we call the onCreate...
        tested.onCreate(mock(Bundle.class));

        // Listener should be in place (Was tested before) so now we need to check that it starts
        //  an activity.
        doNothing().when(tested).startActivity((Intent) any());
        doNothing().when(tested).finish();  // We should also test this to be called in a new test.
        captor.getValue().onClick(mockButton);
        verify(tested).startActivity((Intent) any());
    }
}