JMockit实践--（3）Expectations

声明：

Author：赵志乾

Date：2017-8-6

Declaration：All Right Reserved！！！

    1、在给定的测试中，一个expectation代表对一个特定的、被mocked的方法/构造函数的一组调用。它可能会涵盖测试过程中该方法的多个不同的调用，但这并非强制要求。而方法的一次调用是否匹配特定的expectation，不仅取决于方法签名，还包括传入参数、以及运行时已经匹配的调用次数。我们可以通过指定特定的参数值，使得特定的函数调用匹配特定的expectation。当然，也可以通过指定比较宽泛的匹配条件，使得同一方法的一组调用均能匹配该expectation。下面给出一个示例：

@Testpublic void doBusinessOperationXyz(@Mocked final Dependency mockInstance){   ...   new Expectations() {{      ...      // An expectation for an instance method:      mockInstance.someMethod(1, "test"); result = "mocked";      ...   }};   // A call to code under test occurs here, leading to mock invocations   // that may or may not match specified expectations.}

    该示例给出的是Dependency#someMethod(int, String)方法的expectation，并且需要通过特定的参数匹配方法调用。

2、录制、重放、验证三阶段

    测试过程通常可以划分出三个顺序执行的阶段，如下例所示：

@Testpublic void someTestMethod(){   // 1. Preparation: whatever is required before the code under test can be exercised.   ...   // 2. The code under test is exercised, usually by calling a public method.   ...   // 3. Verification: whatever needs to be checked to make sure the code exercised by   //    the test did its job.   ...}

    首先是准备阶段，在该阶段主要是创建/获取测试过程中需要的对象和数据项。之后是在测试条件下执行代码。最后是结果的验证，即将执行结果和预期结果进行对比。而在基于行为测试（即包含mocked类型）的上下文中，我们通常会将测试过程划分为下面的三个阶段。

    首先是录制阶段，其主要是在mocked方法被调之前对其调用行为进行录制，即完成测试的准备工作。其次是重放阶段，该阶段是指代码执行过程中，如果mocked的方法被调用，将会重放前一阶段录制的行为，即mocked方法表现出预期的行为。最后是验证阶段，该阶段是在测试验证过程中发生，主要是验证mocked方法的调用和我们预期的是否一致。下面给出了使用JMockit的基于行为的测试模板：

import mockit.*;... other imports ...public class SomeTest{   // Zero or more "mock fields" common to all test methods in the class:   @Mocked Collaborator mockCollaborator;   @Mocked AnotherDependency anotherDependency;   ...   @Test   public void testWithRecordAndReplayOnly(mock parameters)   {      // Preparation code not specific to JMockit, if any.      new Expectations() {{ // an "expectation block"         // One or more invocations to mocked types, causing expectations to be recorded.         // Invocations to non-mocked types are also allowed anywhere inside this block         // (though not recommended).      }};      // Unit under test is exercised.      // Verification code (JUnit/TestNG assertions), if any.   }   @Test   public void testWithReplayAndVerifyOnly(mock parameters)   {      // Preparation code not specific to JMockit, if any.      // Unit under test is exercised.      new Verifications() {{ // a "verification block"         // One or more invocations to mocked types, causing expectations to be verified.         // Invocations to non-mocked types are also allowed anywhere inside this block         // (though not recommended).      }};      // Additional verification code, if any, either here or before the verification block.   }   @Test   public void testWithBothRecordAndVerify(mock parameters)   {      // Preparation code not specific to JMockit, if any.      new Expectations() {{         // One or more invocations to mocked types, causing expectations to be recorded.      }};      // Unit under test is exercised.      new VerificationsInOrder() {{ // an ordered verification block         // One or more invocations to mocked types, causing expectations to be verified         // in the specified order.      }};      // Additional verification code, if any, either here or before the verification block.   }}

    注意：一个测试可以包含任意数量的expectation块，甚至可以不包含。

    事实上，匿名内部类可以定界代码块，这可以让我们充分利用IDE中代码折叠的特性，如下面的这张图片所示：

注：本博客中的实例代码均来自于JMockit官方教程。