MyClass.java

public class MyClass {
  
	private MyDatabase myDatabase;

	public String getCustomerName(long customerNo) {
		System.out.println("getCustomerName() is called!");
		return myDatabase.query(customerNo)+"_FROM_DATABASE";
	}

	public MyDatabase getMyDatabase() {
		return myDatabase;
	}

	public void setMyDatabase(MyDatabase myDatabase) {
		this.myDatabase = myDatabase;
	}
}

MyClassTest.java

import static org.mockito.Matchers.anyLong;
import static org.junit.Assert.*;
import static org.mockito.Mockito.*;

import org.junit.After;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.runners.MockitoJUnitRunner;

import com.MyClass;
import com.MyDatabase;

@RunWith(MockitoJUnitRunner.class)
public class MyClassTest {

	@BeforeClass
	public static void beforeClass() {
		System.out.println("Tests are going to start now!");
	}

	@Before
	public void before() {
		System.out.println("******************************");
		System.out.println("");

	}

	@After
	public void after() {
		System.out.println("");
	}

	@Test
	public void testMockWithWhen() {
		System.out.println("---testMockWithWhen started---");

		MyClass mockedClass = mock(MyClass.class);
		when(mockedClass.getCustomerName(anyLong())).thenReturn("John");

		String actualCustomerName = mockedClass.getCustomerName(1000);
		String expectedCustomerName = "John";

		assertEquals(expectedCustomerName, actualCustomerName);

		System.out.println("---testMockWithWhen finished---");
	};

	@Test
	public void testMockWithDoReturn() {
		System.out.println("---testMockWithDoReturn started---");

		MyClass mockedClass = mock(MyClass.class);
		doReturn("John").when(mockedClass).getCustomerName(anyLong());

		String actualCustomerName = mockedClass.getCustomerName(1000);
		String expectedCustomerName = "John";

		assertEquals(expectedCustomerName, actualCustomerName);

		System.out.println("---testMockWithDoReturn finished---");
	};

	@Test
	public void testSpyWithWhen() {
		System.out.println("---testSpyWithWhen started---");

		MyClass mockedClass = spy(MyClass.class);
		mockedClass.setMyDatabase(new MyDatabase());
		when(mockedClass.getCustomerName(anyLong())).thenReturn("John");

		String actualCustomerName = mockedClass.getCustomerName(1000);
		String expectedCustomerName = "John";

		assertEquals(expectedCustomerName, actualCustomerName);

		System.out.println("---testSpyWithWhen finished---");
	};

	@Test
	public void testSpyWithDoReturn() {
		System.out.println("---testSpyWithDoReturn started---");

		MyClass mockedClass = spy(MyClass.class);
		// not necessary this time mockedClass.setMyDatabase(new MyDatabase());
		doReturn("John").when(mockedClass).getCustomerName(anyLong());

		String actualCustomerName = mockedClass.getCustomerName(1000);
		String expectedCustomerName = "John";

		assertEquals(expectedCustomerName, actualCustomerName);

		System.out.println("---testSpyWithDoReturn finished---");
	};

	@Test
	public void testMockDependencyWithWhen() {

		System.out.println("---testMockDependencyWithWhen started---");

		MyDatabase mockedDatabase = mock(MyDatabase.class);
		when(mockedDatabase.query(anyLong())).thenReturn("John");

		MyClass myClass = new MyClass();
		myClass.setMyDatabase(mockedDatabase);

		String actualCustomerName = myClass.getCustomerName(1000);

		/** IMPORTANT **/
		String expectedCustomerName = "John_FROM_DATABASE";

		assertEquals(expectedCustomerName, actualCustomerName);

		System.out.println("---testMockDependencyWithWhen finished---");
	};

	@Test
	public void testMockDependencyWithDoReturn() {

		System.out.println("---testMockDependencyWithDoReturn started---");

		MyDatabase mockedDatabase = mock(MyDatabase.class);
		doReturn("John").when(mockedDatabase).query(anyLong());

		MyClass myClass = new MyClass();
		myClass.setMyDatabase(mockedDatabase);

		String actualCustomerName = myClass.getCustomerName(1000);

		/** IMPORTANT **/
		String expectedCustomerName = "John_FROM_DATABASE";

		assertEquals(expectedCustomerName, actualCustomerName);

		System.out.println("---testMockDependencyWithDoReturn finished---");
	};

	@Test
	public void testSpyDependencyWithWhen() {

		System.out.println("---testSpyDependencyWithWhen started---");

		MyDatabase mockedDatabase = spy(new MyDatabase());
		when(mockedDatabase.query(anyLong())).thenReturn("John");

		MyClass myClass = new MyClass();
		myClass.setMyDatabase(mockedDatabase);

		String actualCustomerName = myClass.getCustomerName(1000);

		/** IMPORTANT **/
		String expectedCustomerName = "John_FROM_DATABASE";

		assertEquals(expectedCustomerName, actualCustomerName);

		System.out.println("---testSpyDependencyWithWhen finished---");
	};

	@Test
	public void testSpyDependencyWithDoReturn() {
		System.out.println("---testSpyDependencyWithDoReturn started---");

		MyDatabase mockedDatabase = spy(new MyDatabase());
		doReturn("John").when(mockedDatabase).query(anyLong());

		MyClass myClass = new MyClass();
		myClass.setMyDatabase(mockedDatabase);

		String actualCustomerName = myClass.getCustomerName(1000);

		/** IMPORTANT **/
		String expectedCustomerName = "John_FROM_DATABASE";

		assertEquals(expectedCustomerName, actualCustomerName);

		System.out.println("---testSpyDependencyWithDoReturn finished---");
	};

}

MyDatabase.java

public class MyDatabase {

	public String query(long customerNo) {
		// TODO implement
		System.out.println("query() is called!");
		return null;
	}

}

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>MockitoTutorial</groupId>
	<artifactId>MockitoTutorial</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>war</packaging>
	<properties>
		<powermock.version>1.7.1</powermock.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.11</version>
			<scope>test</scope>
		</dependency>

		<dependency>
			<groupId>org.powermock</groupId>
			<artifactId>powermock-module-junit4</artifactId>
			<version>${powermock.version}</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.powermock</groupId>
			<artifactId>powermock-api-mockito</artifactId>
			<version>${powermock.version}</version>
			<scope>test</scope>
		</dependency>


	</dependencies>
	<build>
		<sourceDirectory>src</sourceDirectory>
		<testSourceDirectory>test</testSourceDirectory>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.3</version>
				<configuration>
					<source>1.8</source>
					<target>1.8</target>
				</configuration>
			</plugin>
			<plugin>
				<artifactId>maven-war-plugin</artifactId>
				<version>2.6</version>
				<configuration>
					<warSourceDirectory>WebContent</warSourceDirectory>
					<failOnMissingWebXml>false</failOnMissingWebXml>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>