repositories { jcenter() }dependencies { testCompile "org.mockito:mockito-core:1.+" }

apply plugin: 'java'apply plugin: 'idea'sourceCompatibility = 1.5version = '1.0'repositories {    mavenCentral()    jcenter()}dependencies {    testCompile group: 'junit', name: 'junit', version: '4.11'    testCompile "org.mockito:mockito-core:1.8.5"}

package com.mengdd.examples.mockito;public class HelloWorld {    PRivate MyRobot mRobot;    public MyRobot getRobot() {        return mRobot;    }    public void setRobot(MyRobot robot) {        this.mRobot = robot;    }    /**     * This is the method we want to test.     * When there is an robot, this method return the robot's information     * otherwise, return some sorry text     */    public String sayHello() {        MyRobot robot = getRobot();        if (null != robot) {            return robot.getSomeInfo();        }        return "No robot here, sorry!";    }    /**     * MyRobot class     */    public static class MyRobot {        /**         * Get some information from somewhere, the implementation may varies         */        public String getSomeInfo() {            return "Hello World -- From robot";        }    }}

package com.mengdd.examples.mockito;import org.junit.Test;import static org.hamcrest.CoreMatchers.is;import static org.junit.Assert.assertThat;import static org.mockito.Mockito.mock;import static org.mockito.Mockito.when;public class HelloWorldTest {    @Test    public void testSayHelloWhenThereIsRobot() throws Exception {        // We want to test the sayHello() method in the class HelloWorld.        // But we don't care about how MyRobot get its information.(We can treat it as external interface).        // Maybe the robot rely on many complicated things.(Although it's simple in this case.)        // And when the robot's actions change in the future, we don't need to change this test case.        // We can mock the MyRobot's action to make it simple and just test whether sayHello() can do its own work.        // Mock steps        HelloWorld.MyRobot robot = mock(HelloWorld.MyRobot.class); // Mock MyRobot class        String mockInfo = "some mock info";        when(robot.getSomeInfo()).thenReturn(mockInfo); // Set behavior for mock object        // real object        HelloWorld helloWorld = new HelloWorld();//This is the real objec we want to test        helloWorld.setRobot(robot);//set the mock robot to real object        // execute the target method we want to test        String result = helloWorld.sayHello();        // assert the result is what we want to have        assertThat(result, is(mockInfo));    }}

@Testpublic void testSayHelloWhenThereIsNoRobot() throws Exception {    HelloWorld helloWorld = new HelloWorld();    helloWorld.setRobot(null);    String result = helloWorld.sayHello();    assertThat(result, is("No robot here, sorry!"));}