使用Mockito进行Java的Mock测试
准备
本文需要Java和Junit基础，可参考：使用Junit进行单元测试教程，Java程序设计简介。
项目地址：https://github.com/mockito/mockito。
主页： http://mockito.org/。
测试替身
测试替身用于消除单元测试的依赖。
dummy用于传递，不会真正使用，例如用于填充的方法的参数列表。
Fake有简单实现，但通常被简化，比如在内存数据库，而不是真正的数据库中使用。
Stub是接口或类中部分实现，测试时使用其实例，通常有回应，也可能记录调用信息。
Mock对象是接口或类假实现，定义某些方法的输出。
参考资料：http://martinfowler.com/articles/mocksArentStubs.html。
通常首选Mock。Mock框架让你在运行时创建模拟对象，并定义他们的行为。Python中的unittest、pytest、nose等测试框架mock功能做得相当强大。Java的mock功能较弱，Junit需要借助外部包来mock，mock功能也远不及pytest。Java知名的Mock框架有：
jMock(http://jmock.org/): 3年没有更新，对Java7,8支持不好，不支持安卓。
EasyMock(http://easymock.org/): 所有测试都要基于interface，额外增加工作量。支持安卓。
Mockito(https://github.com/mockito/mockito): 易学易用，支持安卓，但是不支持static等方法。
powermock(https://github.com/jayway/powermock)基于Mockitto和EasyMock，自定义类加载器和字节码处理，支持static、构建方法、 final类和方法等Mock。为Java Mock测试的首选。
安装
Eclipse jar包安装(不推荐)
Eclipse ADT安装Mockito的方法：在工程的libs目录中添加dexmaker-1.4.jar、dexmaker-dx-1.2.jar、dexmaker-mockito-1.4.jar、mockito-core-1.10.19.jar. 下载地址参考：
http://central.maven.org/maven2/com/google/dexmaker/dexmaker-dx/1.2/dexmaker-dx-1.2.jar
https://oss.sonatype.org/service/local/repositories/releases/content/com/crittercism/dexmaker/dexmaker/1.4/dexmaker-1.4.jar
https://oss.sonatype.org/service/local/repositories/releases/content/com/crittercism/dexmaker/dexmaker-mockito/1.4/dexmaker-mockito-1.4.jar
http://mockito.org/
非安卓系统的安装：
mockito-core-1.10.19.jar objenesis-2.1.jar
ItellliJ IDEA的安装：File - Project Settings - Modules:
其他安装方式
Gradle中的设置如下：
repositories { jcenter() }
dependencies { testCompile "org.mockito:mockito-core:1.+" }
Maven中可以用依赖搞定，在http://search.maven.org/搜索"org.mockito"和"mockito-core"可以找到对应的POM入口。
<dependency> <groupId>org.mockito</groupId> <artifactId>mockito-all</artifactId> <version>1.10.19</version> </dependency>
快速入门
Mockito支持用静态mock()创建mock对象。通过静态导入，您可以在指定类的情况下调用静态成员(方法和成员)。verify()方法用于确认模拟的方法已经调用。用来指定条件和对应的返回值。如果指定多个值，会依次返回。然后最后一个指定的值返回。when(....).thenReturn(....)anyString或。anyInt实现了类似通配符的功能
下面例子，我们基于MyClass.java:
package first;
public class MyClass {
public int multiply(int x, int y) {、
// the following is just an example
if (x > 999) {
throw new IllegalArgumentException("X should be less than 1000");
}
return x / y;
}
}
测试代码MyClassTest.java
package first;
import org.junit.Test;
import static org.mockito.Mockito.*;
import static org.junit.Assert.*;
import static org.junit.Assert.assertEquals;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import java.util.Iterator;
public class MyClassTest {
@Test(expected = IllegalArgumentException.class)
public void testExceptionIsThrown() {
MyClass tester = new MyClass();
tester.multiply(1000, 5);
}
@Test
public void testMultiply() {
MyClass tester = new MyClass();
assertEquals("10 x 5 must be 50", 2, tester.multiply(10, 5));
}
@Test
public void test1() {
// create mock
MyClass test = mock(MyClass.class);
// define return value for method getUniqueId()
when(test.multiply(3, 3)).thenReturn(9);
// use mock in test....
assertEquals(test.multiply(3,3), 9);
}
// Demonstrates the return of multiple values
@Test
public void testMoreThanOneReturnValue() {
Iterator i= mock(Iterator.class);
when(i.next()).thenReturn("Mockito").thenReturn("rocks");
String result=i.next()+" "+i.next();
//assert
assertEquals("Mockito rocks", result);
}
// this test demonstrates how to return values based on the input
@Test
public void testReturnValueDependentOnMethodParameter() {
Comparable c= mock(Comparable.class);
when(c.compareTo("Mockito")).thenReturn(1);
when(c.compareTo("Eclipse")).thenReturn(2);
//assert
assertEquals(1, c.compareTo("Mockito"));
}
// this test demonstrates how to return values independent of the input value
@Test
public void testReturnValueInDependentOnMethodParameter2() {
Comparable c= mock(Comparable.class);
when(c.compareTo(anyInt())).thenReturn(-1);
//assert
assertEquals(-1 ,c.compareTo(9));
}
}
方法testExceptionIsThrown和testMultiply是正常的Junit测试。test1为返回模拟值，testMoreThanOneReturnValue返回2个值，testReturnValueDependentOnMethodParameter根据输入返回值，testReturnValueInDependentOnMethodParameter使用了通配符。另外还可以基于条件mock：
@Test
public void testReturnValueInDependentOnMethodParameter() {
Comparable c= mock(Comparable.class);
when(c.compareTo(isA(Todo.class))).thenReturn(0);
//assert
Todo todo = new Todo(5);
assertEquals(todo ,c.compareTo(new Todo(1)));
}
doReturn(...).when(...).methodCall的工作方法类似，适用于void方法。
doThrow适合返回void的方法的异常处理:
@Test(expected=IOException.class)
public void testForIOException() throws IOException {
// create an configure mock
OutputStream mockStream = mock(OutputStream.class);
doThrow(new IOException()).when(mockStream).close();
// use mock
OutputStreamWriter streamWriter= new OutputStreamWriter(mockStream);
streamWriter.close();
}
股票交易测试实例
下面实例买卖股票，类有：
下面实例买卖股票，类有： Stock、MarketWatcher、Portfolio和StockBroker。MarketWatcher返回当前股票价格、Portfolio统计利润。StockBroker的perform在获利10%以上卖出。测试需要portfolio总返回10，股价返回100。
使用的mock有几种方法：
1，使用完整的Mockito类调用。
import org.mockito.Mockito;
public class StockBrokerTest {
MarketWatcher marketWatcher = Mockito.mock(MarketWatcher.class);
Portfolio portfolio = Mockito.mock(Portfolio.class);
}
2，使用静态导入：
import static org.mockito.Mockito.mock;
public class StockBrokerTest {
MarketWatcher marketWatcher = mock(MarketWatcher.class);
Portfolio portfolio = mock(Portfolio.class);
}
3，注解类成员
import org.mockito.Mock;
public class StockBrokerTest {
@Mock
MarketWatcher marketWatcher;
@Mock
Portfolio portfolio;
}
有个前提：需要初始化mock。可以使用 MockitoAnnotations.initMocks(this)或者 MockitoJUnitRunner。示例分别如下：
import static org.junit.Assert.assertEquals;
import org.mockito.MockitoAnnotations;
public class StockBrokerTest {
@Mock
MarketWatcher marketWatcher;
@Mock
Portfolio portfolio;
@Before
public void setUp() {
MockitoAnnotations.initMocks(this);
}
@Test
public void sanity() throws Exception {
assertNotNull(marketWatcher);
assertNotNull(portfolio);
}
}
import org.mockito.runners.MockitoJUnitRunner;
@RunWith(MockitoJUnitRunner.class)
public class StockBrokerTest {
@Mock
MarketWatcher marketWatcher;
@Mock
Portfolio portfolio;
@Test
public void sanity() throws Exception {
assertNotNull(marketWatcher);
assertNotNull(portfolio);
}
}
Mockito不能mock或spy final类和方法、static及private方法、enum、 equals()和hashCode()、原始类型和匿名类。PowerMockito解决了上述问题。一般很好的封装，不需要使用PowerMockito。
mock对象有默认值，Boolean返回false，对象返回null，数值返回零等。
when后面的使用方法:
• thenReturn(value to be returned)：返回指定值。
• thenThrow(throwable to be thrown)：抛出指定异常。
• thenAnswer(Answer answer) :返回指定逻辑，Answer是个接口。
• thenCallRealMethod(): 调用指定方法。
verify()可以接收 org.mockito.internal.verification.Times作为参数。verify可以配合使用的方法如下：
• times(int wantedNumberOfInvocations)
• never()
• atLeastOnce()
• atLeast(int minNumberOfInvocations)
• atMost(int maxNumberOfInvocations)
• only(): 只调用该方法。
• timeout(int millis) :
代码如下：
public class MarketWatcher {
public Stock getQuote(Object symbol) {
// TODO Auto-generated method stub
return null;
}
}
import java.math.BigDecimal;
public class Portfolio {
public BigDecimal getAvgPrice(Stock stock) {
// TODO Auto-generated method stub
return null;
}
public void sell(Stock stock, int i) {
// TODO Auto-generated method stub
}
public void buy(Stock stock) {
// TODO Auto-generated method stub
}
}
import java.math.BigDecimal;
public class Stock {
public Stock(String string, String string2, BigDecimal bigDecimal) {
// TODO Auto-generated constructor stub
}
public Object getSymbol() {
// TODO Auto-generated method stub
return null;
}
public BigDecimal getPrice() {
// TODO Auto-generated method stub
return BigDecimal.valueOf(100.48);
}
}
import java.math.BigDecimal;
public class StockBroker {
private final static BigDecimal LIMIT = new BigDecimal("0.10");
private final MarketWatcher market;
public StockBroker(MarketWatcher market) {
this.market = market;
}
public void perform(Portfolio portfolio, Stock stock) {
Stock liveStock = market.getQuote(stock.getSymbol());
BigDecimal avgPrice = portfolio.getAvgPrice(stock);
BigDecimal priceGained =
liveStock.getPrice().subtract(avgPrice);
BigDecimal percentGain = priceGained.divide(avgPrice);
if(percentGain.compareTo(LIMIT) > 0) {
portfolio.sell(stock, 10);
}else if(percentGain.compareTo(LIMIT) < 0){
portfolio.buy(stock);
}
}
}
import static org.junit.Assert.assertNotNull;
import static org.mockito.Matchers.anyString;
import static org.mockito.Matchers.isA;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.verifyZeroInteractions;
import static org.mockito.Mockito.verifyNoMoreInteractions;
import static org.mockito.Mockito.when;
import java.math.BigDecimal;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;
@RunWith(MockitoJUnitRunner.class)
public class StockBrokerTest {
@Mock MarketWatcher marketWatcher;
@Mock Portfolio portfolio;
StockBroker broker;
@Before
public void setUp() {
broker = new StockBroker(marketWatcher);
}
@Test
public void when_ten_percent_gain_then_the_stock_is_sold() {
//Portfolio's getAvgPrice is stubbed to return $10.00
when(portfolio.getAvgPrice(isA(Stock.class))).thenReturn(new BigDecimal("10.00"));
//A stock object is created with current price $11.20
Stock aCorp = new Stock("A", "A Corp", new BigDecimal("11.20"));
//getQuote method is stubbed to return the stock
when(marketWatcher.getQuote(anyString())).thenReturn(aCorp);
//perform method is called, as the stock price increases
// by 12% the broker should sell the stocks
broker.perform(portfolio, aCorp);
//verifying that the broker sold the stocks
verify(portfolio).sell(aCorp,10);
}
@Test
public void verify_zero_interaction() {
verifyZeroInteractions(marketWatcher,portfolio);
}
@Test(expected = IllegalStateException.class)
public void throwsException() throws Exception {
when(portfolio.getAvgPrice(isA(Stock.class))).thenThrow(
new IllegalStateException("Database down"));
portfolio.getAvgPrice(new Stock(null, null, null));
}
}
verifyNoMoreInteractions(Object mocks)，确认没有关系。
void方法的发送异常方式：doThrow(exception).when(mock).voidmethod(arguments);
参考资料：
http://www.vogella.com/tutorials/Mockito/article.html
书籍：Mockito for Spring - 2015
书籍：Test-Driven Development with Mockito
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