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first
System.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element
System.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* methods
spy.add("one");
spy.add("two");
//prints "one" - the first element of a list
System.out.println(spy.get(0));
//size() method was stubbed - 100 is printed
System.out.println(spy.size());
//optionally, you can verify
verify(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 span
verify(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 span
verify(mock, timeout(100).times(2)).someMethod();
//passes when someMethod() is called *at least* 2 times within given time span
verify(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();
