单元测试 - 模拟域对象

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2023-12-01

遇到了另一个常见的问题,同时为Spring Batch编写单元测试和集成测试组件是如何模拟域对象。一个很好的例子是StepExecutionListener,如下所示:

public class NoWorkFoundStepExecutionListener extends StepExecutionListenerSupport {
    public ExitStatus afterStep(StepExecution stepExecution) {
        if (stepExecution.getReadCount() == 0) {
            throw new NoWorkFoundException("Step has not processed any items");
        }
        return stepExecution.getExitStatus();
    }
}

上面的监听是框架提供的，并且它检测到stepExecution的read count是为空的，因此它表示没有工作要做。虽然这个例子相当简单，当试图单元测试类的时候它解释了可能遇到的问题类型,实现接口验证Spring Batch 域对象。考虑到上面的侦听器的单元测试:

private NoWorkFoundStepExecutionListener tested = new NoWorkFoundStepExecutionListener();
@Test
public void testAfterStep() {
    StepExecution stepExecution = new StepExecution("NoProcessingStep",
                new JobExecution(new JobInstance(1L, new JobParameters(),
                                 "NoProcessingJob")));
    stepExecution.setReadCount(0);
    try {
        tested.afterStep(stepExecution);
        fail();
    } catch (NoWorkFoundException e) {
        assertEquals("Step has not processed any items", e.getMessage());
    }
}

因为Spring Batch域模型遵循良好的面向对象原则，StepExecution需要一个JobExecution，JobExecution需要一个JobInstance和JobParameters为了创建一个有效的StepExecution。虽然这是很好的可靠的域模型,为了冗长的单元测试创建存根对象。为了解决这个问题，Spring Batch测试模块引入一个工厂来创建域对象:MetaDataInstanceFactory，把这个给到工厂，更新后的单元测试可以更简洁：

private NoWorkFoundStepExecutionListener tested = new NoWorkFoundStepExecutionListener();
@Test
public void testAfterStep() {
    StepExecution stepExecution = MetaDataInstanceFactory.createStepExecution();
    stepExecution.setReadCount(0);
    try {
        tested.afterStep(stepExecution);
        fail();
    } catch (NoWorkFoundException e) {
        assertEquals("Step has not processed any items", e.getMessage());
    }
}

上面的方法为了创建一个简单的StepExecution，它仅仅是便利的方法中可用的工厂。完整的方法清单可以在Javadoc找到