java - 如何在 JUnit @Before 方法以及测试方法中使用 EasyMock 对象

Question

我尝试将 EasyMock 与 JUnit 一起使用，但在对 JUnit 4 @Before 方法中的模拟依赖项进行调度方法调用时遇到了困难。

在下面的示例中，测试类 MockWithBeforeTest 正在测试类 ClassUnderTest。 Dependency 被传递到 ClassUnderTest 的构造函数，其中调用 Dependency 的方法之一，返回初始化 所需的值被测类。对于所有测试来说，初始化 ClassUnderTest 的过程都是相同的，因此我使用 JUnit 4 @Before 注释来修饰 ClassUnderTest#setUp 方法。

测试方法 ClassUnderTest#getDerived 时，我们期望调用模拟的 Dependency 实例来返回一个值，我们在方法 MockWithBeforeTest#testGetDerived 中安排该值。但是，此测试意外失败，并出现错误 Unexpected method call Dependency.getB()，尽管此调用是在 MockWithBeforeTest#testGetDerived 中安排的。

我应该如何修改示例代码以使 MockWithBeforeTest#testGetDerived 通过？

示例代码

import static org.easymock.EasyMock.expect;
import static org.easymock.EasyMock.replay;
import static org.easymock.EasyMock.verify;
import static org.junit.Assert.assertEquals;
import org.easymock.EasyMockRule;
import org.easymock.Mock;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;

public class MockWithBeforeTest {

  @Rule
  public EasyMockRule rule = new EasyMockRule(this);

  @Mock
  private Dependency dependency;

  private ClassUnderTest classUnderTest;

  @Before
  public void setUp() {
    expect(this.dependency.getA()).andReturn(2);
    replay(this.dependency);

    this.classUnderTest = new ClassUnderTest(this.dependency);
    verify(this.dependency);

  }

  @Test
  public void testGetDerived() {
    expect(this.dependency.getB()).andReturn(3);
    replay(this.dependency);

    assertEquals(6, this.classUnderTest.getDerived(1));
    verify(this.dependency);
  }

}

class ClassUnderTest {
  private int a;
  private Dependency dependency;

  ClassUnderTest(Dependency dependency) {
    this.a = dependency.getA();
    this.dependency = dependency;
  }

  void setA(int val) {
    this.a = val;
  }

  int getDerived(int val) {
    return val * this.a * this.dependency.getB();
  }

}

class Dependency {
  private int a;
  private int b;

  Dependency(int a, int b) {
    this.a = a;
    this.b = b;
  }

  int getA() {
    return this.a;
  }

  int getB() {
    return this.b;
  }

}

堆栈跟踪

java.lang.AssertionError: 
  Unexpected method call Dependency.getB():
    at org.easymock.internal.MockInvocationHandler.invoke(MockInvocationHandler.java:44)
    at org.easymock.internal.ObjectMethodsFilter.invoke(ObjectMethodsFilter.java:101)
    at org.easymock.internal.ClassProxyFactory$MockMethodInterceptor.intercept(ClassProxyFactory.java:97)
    at Dependency$$EnhancerByCGLIB$$6d3a4341.getB(<generated>)
    at MockWithBeforeTest.testGetDerived(MockWithBeforeTest.java:33)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.easymock.internal.EasyMockStatement.evaluate(EasyMockStatement.java:43)
    at org.junit.rules.RunRules.evaluate(RunRules.java:20)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:89)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)

为什么不创建一个 Dependency 实例来传递给构造函数？

上面给出的示例代表了一个普遍问题，其中传递给被测类的依赖关系比依赖关系复杂得多。

对设计问题的推测

我注意到这样一个事实:被测类实现的详细信息通过模拟依赖项上的预定方法泄漏到测试类中。然而，我对模拟框架的经验不足，无法判断这是模拟不可避免的副作用，还是我的设计中存在缺陷的症状。任何有关这方面的指导将不胜感激。

软件版本信息

• Java:1.8.0_201
• JUnit:4.12
• EasyMock:4.2

Answer 1

与同事进行更多研究和讨论得出了解决方案。我错过的步骤是重置模拟的 Dependency 对象 using EasyMock.reset(this.dependency) 允许在测试方法中添加额外的预期调用。固定的MockWithBeforeTest是

public class MockWithBeforeTest {

  @Rule
  public EasyMockRule rule = new EasyMockRule(this);

  @Mock
  private Dependency dependency;

  private ClassUnderTest classUnderTest;

  @Before
  public void setUp() {
    expect(this.dependency.getA()).andReturn(2);
    replay(this.dependency);

    this.classUnderTest = new ClassUnderTest(this.dependency);
    verify(this.dependency);
    reset(this.dependency); // Allow additional expected method calls to be specified
                            // in the test methods

  }

  @Test
  public void testGetDerived() {
    expect(this.dependency.getB()).andReturn(3);
    replay(this.dependency);

    assertEquals(6, this.classUnderTest.getDerived(1));
    verify(this.dependency);
  }

}