Mockito浅谈

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Mockito简介

• 什么是mock？
  在软件开发的世界之外, “mock”一词是指模仿或者效仿。 因此可以将“mock”理解为一个替身，替代者. 在软件开发中提及”mock”，通常理解为模拟对象或者Fake。

• 为什么需要Mock?
  Mock是为了解决units之间由于耦合而难于被测试的问题。所以mock object是unit test的一部分。

Mock的好处是什么?

• 提前创建测试，TDD（测试驱动开发）

  这是个最大的好处吧。如果你创建了一个Mock那么你就可以在service接口创建之前写Service Tests了，这样你就能在开发过程中把测试添加到你的自动化测试环境中了。换句话说，模拟使你能够使用测试驱动开发。

• 团队可以并行工作

  这类似于上面的那点；为不存在的代码创建测试。但前面讲的是开发人员编写测试程序，这里说的是测试团队来创建。当还没有任何东西要测的时候测试团队如何来创建测试呢？模拟并针对模拟测试！这意味着当service借口需要测试时，实际上QA团队已经有了一套完整的测试组件；没有出现一个团队等待另一个团队完成的情况。这使得模拟的效益型尤为突出了。

• 你可以创建一个验证或者演示程序。

  由于Mocks非常高效，Mocks可以用来创建一个概念证明，作为一个示意图，或者作为一个你正考虑构建项目的演示程序。这为你决定项目接下来是否要进行提供了有力的基础，但最重要的还是提供了实际的设计决策。

• 为无法访问的资源编写测试

  这个好处不属于实际效益的一种，而是作为一个必要时的“救生圈”。有没有遇到这样的情况？当你想要测试一个service接口，但service需要经过防火墙访问，防火墙不能为你打开或者你需要认证才能访问。遇到这样情况时，你可以在你能访问的地方使用MockService替代，这就是一个“救生圈”功能。

• Mock 可以交给用户

  在有些情况下，某种原因你需要允许一些外部来源访问你的测试系统，像合作伙伴或者客户。这些原因导致别人也可以访问你的敏感信息，而你或许只是想允许访问部分测试环境。在这种情况下，如何向合作伙伴或者客户提供一个测试系统来开发或者做测试呢？最简单的就是提供一个mock，无论是来自于你的网络或者客户的网络。soapUI mock非常容易配置，他可以运行在soapUI或者作为一个war包发布到你的java服务器里面。

• 隔离系统

  有时，你希望在没有系统其他部分的影响下测试系统单独的一部分。由于其他系统部分会给测试数据造成干扰，影响根据数据收集得到的测试结论。使用mock你可以移除掉除了需要测试部分的系统依赖的模拟。当隔离这些mocks后，mocks就变得非常简单可靠，快速可预见。这为你提供了一个移除了随机行为，有重复模式并且可以监控特殊系统的测试环境。

Mockito使用示例

模拟对象

// 模拟LinkedList 的一个对象  LinkedList mockedList = mock(LinkedList.class);// 此时调用get方法，会返回null，因为还没有对方法调用的返回值做模拟System.out.println(mockedList.get(0));  

模拟方法调用的返回值

// 模拟获取第一个元素时，返回字符串first。  给特定的方法调用返回固定值在官方说法中称为stub。when(mockedList.get(0)).thenReturn("first");// 此时打印输出firstSystem.out.println(mockedList.get(0));  

模拟方法调用抛出异常

// 模拟获取第二个元素时，抛出RuntimeException  when(mockedList.get(1)).thenThrow(new RuntimeException());// 此时将会抛出RuntimeException  System.out.println(mockedList.get(1)); 

如果一个函数没有返回值类型，那么可以使用此方法模拟异常抛出

doThrow(new RuntimeException("clear exception")).when(mockedList).clear();mockedList.clear();

模拟调用方法时的参数匹配

// anyInt()匹配任何int参数，这意味着参数为任意值，其返回值均是element  when(mockedList.get(anyInt())).thenReturn("element");// 此时打印是elementSystem.out.println(mockedList.get(999)); 

模拟方法调用次数

// 调用add一次mockedList.add("once"); // 下面两个写法验证效果一样，均验证add方法是否被调用了一次verify(mockedList).add("once");verify(mockedList, times(1)).add("once");  

校验行为

 // mock creation List mockedList = mock(List.class); // using mock object mockedList.add("one"); mockedList.clear(); //verification verify(mockedList).add("one"); verify(mockedList).clear();

模拟方法调用(Stubbing)

 //You can mock concrete classes, not just interfaces LinkedList mockedList = mock(LinkedList.class); //stubbing when(mockedList.get(0)).thenReturn("first"); when(mockedList.get(1)).thenThrow(new RuntimeException()); //following prints "first" System.out.println(mockedList.get(0)); //following throws runtime exception System.out.println(mockedList.get(1)); //following prints "null" because get(999) was not stubbed System.out.println(mockedList.get(999)); verify(mockedList).get(0);

参数匹配

 //stubbing using built-in anyInt() argument matcher when(mockedList.get(anyInt())).thenReturn("element"); //stubbing using custom matcher (let's say isValid() returns your own matcher implementation): when(mockedList.contains(argThat(isValid()))).thenReturn("element"); //following prints "element" System.out.println(mockedList.get(999)); //you can also verify using an argument matcher verify(mockedList).get(anyInt()); //argument matchers can also be written as Java 8 Lambdas verify(mockedList).add(someString -> someString.length() > 5);

校验方法调用次数

 //using mock mockedList.add("once"); mockedList.add("twice"); mockedList.add("twice"); mockedList.add("three times"); mockedList.add("three times"); mockedList.add("three times"); //following two verifications work exactly the same - times(1) is used by default verify(mockedList).add("once"); verify(mockedList, times(1)).add("once"); //exact number of invocations verification verify(mockedList, times(2)).add("twice"); verify(mockedList, times(3)).add("three times"); //verification using never(). never() is an alias to times(0) verify(mockedList, never()).add("never happened"); //verification using atLeast()/atMost() verify(mockedList, atLeastOnce()).add("three times"); verify(mockedList, atLeast(2)).add("five times"); verify(mockedList, atMost(5)).add("three times");

模拟无返回方法抛出异常

doThrow(new RuntimeException()).when(mockedList).clear();//following throws RuntimeException:mockedList.clear();

校验方法调用顺序

 // A. Single mock whose methods must be invoked in a particular order List singleMock = mock(List.class); //using a single mock singleMock.add("was added first"); singleMock.add("was added second"); //create an inOrder verifier for a single mock InOrder inOrder = inOrder(singleMock); //following will make sure that add is first called with "was added first, then with "was added second" inOrder.verify(singleMock).add("was added first"); inOrder.verify(singleMock).add("was added second"); // B. Multiple mocks that must be used in a particular order List firstMock = mock(List.class); List secondMock = mock(List.class); //using mocks firstMock.add("was called first"); secondMock.add("was called second"); //create inOrder object passing any mocks that need to be verified in order InOrder inOrder = inOrder(firstMock, secondMock); //following will make sure that firstMock was called before secondMock inOrder.verify(firstMock).add("was called first"); inOrder.verify(secondMock).add("was called second"); // Oh, and A + B can be mixed together at will

校验方法是否从未调用

 //using mocks - only mockOne is interacted mockOne.add("one"); //ordinary verification verify(mockOne).add("one"); //verify that method was never called on a mock verify(mockOne, never()).add("two"); //verify that other mocks were not interacted verifyZeroInteractions(mockTwo, mockThree);

快速创建Mock对象

public class ArticleManagerTest {   @Mock private ArticleCalculator calculator;      @Mock private ArticleDatabase database;      @Mock private UserProvider userProvider;      @Before      public void before(){          MockitoAnnotations.initMocks(this);      }}

自定义返回不同结果

when(mock.someMethod("some arg"))   .thenThrow(new RuntimeException())  // 第一次会抛出异常   .thenReturn("foo"); // 第二次会返回这个结果//First call: throws runtime exception:mock.someMethod("some arg"); // 第一次//Second call: prints "foo"System.out.println(mock.someMethod("some arg")); // 第二次//Any consecutive call: prints "foo" as well (last stubbing wins).System.out.println(mock.someMethod("some arg")); // 第n次(n> 2)，依旧以最后返回最后一个配置

对返回结果进行拦截

when(mock.someMethod(anyString())).thenAnswer(new Answer() {    Object answer(InvocationOnMock invocation) {        Object[] args = invocation.getArguments();        Object mock = invocation.getMock();        return "called with arguments: " + args;    }});//the following prints "called with arguments: foo"System.out.println(mock.someMethod("foo"));

Mock函数操作

可以通过doThrow(), doAnswer(), doNothing(), doReturn() and doCallRealMethod() 来自定义函数操作。

暗中调用真实对象

List list = new LinkedList();List spy = spy(list);//optionally, you can stub out some methods:when(spy.size()).thenReturn(100);//using the spy calls *real* methodsspy.add("one");spy.add("two");//prints "one" - the first element of a listSystem.out.println(spy.get(0));//size() method was stubbed - 100 is printedSystem.out.println(spy.size());//optionally, you can verifyverify(spy).add("one");   verify(spy).add("two");

改变默认返回值

Foo mock = mock(Foo.class, Mockito.RETURNS_SMART_NULLS);Foo mockTwo = mock(Foo.class, new YourOwnAnswer());

捕获函数的参数值

ArgumentCaptor<Person> argument = ArgumentCaptor.forClass(Person.class);verify(mock).doSomething(argument.capture());assertEquals("John", argument.getValue().getName());

部分Mock

//you can create partial mock with spy() method:List list = spy(new LinkedList());//you can enable partial mock capabilities selectively on mocks:Foo mock = mock(Foo.class);//Be sure the real implementation is 'safe'.//If real implementation throws exceptions or depends on specific state of the object then you're in trouble.when(mock.someMethod()).thenCallRealMethod();

重置Mock

List mock = mock(List.class);when(mock.size()).thenReturn(10);mock.add(1);reset(mock);//at this point the mock forgot any interactions & stubbing

序列化

List<Object> list = new ArrayList<Object>();List<Object> spy = mock(ArrayList.class, withSettings()                 .spiedInstance(list)                 .defaultAnswer(CALLS_REAL_METHODS)                 .serializable());

检查超时

//passes when someMethod() is called within given time spanverify(mock, timeout(100)).someMethod();//above is an alias to:verify(mock, timeout(100).times(1)).someMethod();//passes when som`eMethod() is called *exactly* 2 times within given time spanverify(mock, timeout(100).times(2)).someMethod();//passes when someMethod() is called *at least* 2 times within given time spanverify(mock, timeout(100).atLeast(2)).someMethod();//verifies someMethod() within given time span using given verification mode//useful only if you have your own custom verification modes.verify(mock, new Timeout(100, yourOwnVerificationMode)).someMethod();

Mock详情

Mockito.mockingDetails(someObject).isMock();Mockito.mockingDetails(someObject).isSpy();