java JUnit @Before 与 @Rule

JUnit @Before vs @Rule

提问by kgf3JfUtW

I understand that,

我明白那个，

• @Beforeand @BeforeClassrun before each test, or the entire test class, respectively
• @Ruleand @ClassRulewraps each test, or the entire test class, respectively.

• @Before并分别@BeforeClass在每个测试或整个测试类之前运行
• @Rule并分别@ClassRule包装每个测试或整个测试类。

Let's say I need to initialize some data before each test method,

假设我需要在每个测试方法之前初始化一些数据，

How do I decide between using @Beforeand @Rule? Under what conditions is one preferred over another?The same question also goes for @BeforeClassvs.@ClassRule.

我如何决定使用@Before和@Rule？在什么条件下一个人比​​另一个人更受欢迎？同样的问题也适用于@BeforeClassvs. @ClassRule。

采纳答案by Quwin

In order to use @Rule, you require a class that implements TestRule(preferred) or MethodRule, as can be read here. Whereas @Beforeand @Afterrequire a new method to be written in every test case, @Ruledoes not because it is only an instantiation of already existing code.

为了使用@Rule，您需要一个实现TestRule（首选） or 的类MethodRule，可以在此处阅读。而@Before和@After需要一种新的方法在每个测试用例来写，@Rule不会因为这只是一个已经存在的代码的实例。

So, if you would use @Beforeand @Afterfor setUp()and tearDown()that you'll be using in many test cases, it is actually a better idea to use @Rulebecause of code reuse. If you have a test case that requires a unique @Beforeand/or @After, then these annotations are preferable.

所以，如果你会使用@Before，并@After为setUp()和tearDown()，你会使用在很多测试案例，它实际上是一个更好的主意，利用@Rule因code reuse。如果您有一个需要唯一@Before和/或的测试用例@After，那么最好使用这些注释。

For a bit more elaborate answer with a couple examples, take a look here. Ajit explains it very well.

有关几个示例的更详细的答案，请查看此处。Ajit 很好地解释了这一点。

回答by kgf3JfUtW

Indeed, as @Quwin suggested, accoridng to JUnit 4.12 API doc,

事实上，正如@Quwin 所建议的，根据JUnit 4.12 API 文档，

TestRulecan do everything that could be done previously with methods annotated with @Before, @After, @BeforeClass, or @AfterClass, but TestRules are (1) more powerful, and (2) more easily shared between projects and classes.

TestRule可以完成以前使用@Before, @After, @BeforeClass, 或 注释的方法可以完成的所有事情@AfterClass，但是TestRules (1) 更强大，并且(2) 更容易在项目和类之间共享。

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Ways that TestRules are more powerful:

方法是TestRules为更强大：

There are known implementing classes of the TestRule, which are some usefuls rules you can use out-of-the-box,

有一些已知的 实现类TestRule，这些是一些可以开箱即用的有用规则，

For examples of how this can be useful, see these provided TestRules, or write your own:

• ErrorCollector: collect multiple errors in one test method
• ExpectedException: make flexible assertions about thrown exceptions
• ExternalResource: start and stop a server, for example
• TemporaryFolder: create fresh files, and delete after test
• TestName: remember the test name for use during the method
• TestWatcher: add logic at events during method execution
• Timeout: cause test to fail after a set time
• Verifier: fail test if object state ends up incorrect

有关这如何有用的示例，请参阅这些提供的 TestRules，或编写您自己的：

• ErrorCollector: 在一种测试方法中收集多个错误
• ExpectedException: 对抛出的异常做出灵活的断言
• ExternalResource：例如启动和停止服务器
• TemporaryFolder: 创建新文件，测试后删除
• TestName: 记住方法中使用的测试名称
• TestWatcher: 在方法执行期间在事件中添加逻辑
• Timeout: 导致测试在设定的时间后失败
• Verifier: 如果对象状态最终不正确，则测试失败

Another benefit of rules, is that multiple rules can be used in a single test case. You may want to use RuleChainto specify the order in which the rules should be run.

规则的另一个好处是可以在单个测试用例中使用多个规则。您可能希望使用RuleChain来指定规则运行的顺序。