@ Before，@ BeforeClass，@ BeforeEach和@BeforeAll之间的区别

本文翻译自：Difference between @Before, @BeforeClass, @BeforeEach and @BeforeAll

What is the main difference between 之间的主要区别是什么

@Before and @BeforeClass @Before和@BeforeClass
- and in JUnit 5 @BeforeEach and @BeforeAll 在JUnit 5中@BeforeEach和@BeforeAll
@After and @AfterClass @After和@AfterClass

According to the JUnit Api @Before is used in the following case: 根据JUnit Api ，在以下情况下使用@Before ：

When writing tests, it is common to find that several tests need similar objects created before they can run. 编写测试时，通常会发现几个测试需要先创建类似的对象，然后才能运行。

Whereas @BeforeClass can be used to establish a database connection. 而@BeforeClass可用于建立数据库连接。 But couldn't @Before do the same? 但是@Before不能一样吗？

#1楼

参考：https://stackoom.com/question/1N9o2/Before-BeforeClass-BeforeEach和-BeforeAll之间的区别

#2楼

The code marked @Before is executed before each test, while @BeforeClass runs once before the entire test fixture. 标有@Before的代码在每次测试之前执行，而@BeforeClass在整个测试夹具之前运行一次。 If your test class has ten tests, @Before code will be executed ten times, but @BeforeClass will be executed only once. 如果您的测试类有十个测试，则@Before代码将执行十次，但是@BeforeClass将仅执行一次。

In general, you use @BeforeClass when multiple tests need to share the same computationally expensive setup code. 通常，当多个测试需要共享相同的计算昂贵的设置代码时，可以使用@BeforeClass 。 Establishing a database connection falls into this category. 建立数据库连接属于此类。 You can move code from @BeforeClass into @Before , but your test run may take longer. 您可以将代码从@BeforeClass移到@Before ，但是您的测试运行可能需要更长的时间。 Note that the code marked @BeforeClass is run as static initializer, therefore it will run before the class instance of your test fixture is created. 注意，标记为@BeforeClass的代码作为静态初始化程序运行，因此它将在创建测试夹具的类实例之前运行。

In JUnit 5 , the tags @BeforeEach and @BeforeAll are the equivalents of @Before and @BeforeClass in JUnit 4. Their names are a bit more indicative of when they run, loosely interpreted: 'before each tests' and 'once before all tests'. 在JUnit 5中，标签@BeforeEach和@BeforeAll与JUnit 4中的@Before和@BeforeClass等效。它们的名称更能指示它们的运行时间，松散地解释为：“每次测试之前”和“一次在所有测试之前”。 '。

#3楼

Difference between each annotation are : 每个注释之间的区别是：

+-------------------------------------------------------------------------------------------------------+
¦                                       Feature                            ¦   Junit 4    ¦   Junit 5   ¦
¦--------------------------------------------------------------------------+--------------+-------------¦
¦ Execute before all test methods of the class are executed.               ¦ @BeforeClass ¦ @BeforeAll  ¦
¦ Used with static method.                                                 ¦              ¦             ¦
¦ For example, This method could contain some initialization code          ¦              ¦             ¦
¦-------------------------------------------------------------------------------------------------------¦
¦ Execute after all test methods in the current class.                     ¦ @AfterClass  ¦ @AfterAll   ¦
¦ Used with static method.                                                 ¦              ¦             ¦
¦ For example, This method could contain some cleanup code.                ¦              ¦             ¦
¦-------------------------------------------------------------------------------------------------------¦
¦ Execute before each test method.                                         ¦ @Before      ¦ @BeforeEach ¦
¦ Used with non-static method.                                             ¦              ¦             ¦
¦ For example, to reinitialize some class attributes used by the methods.  ¦              ¦             ¦
¦-------------------------------------------------------------------------------------------------------¦
¦ Execute after each test method.                                          ¦ @After       ¦ @AfterEach  ¦
¦ Used with non-static method.                                             ¦              ¦             ¦
¦ For example, to roll back database modifications.                        ¦              ¦             ¦
+-------------------------------------------------------------------------------------------------------+

Most of annotations in both versions are same, but few differs. 两个版本中的大多数注释都相同，但几乎没有区别。

Reference 参考

Order of Execution. 执行顺序。

Dashed box -> optional annotation. 虚线框->可选注释。

#4楼

Before and BeforeClass in JUnit JUnit中的BeforeClass和BeforeClass

The function @Before annotation will be executed before each of test function in the class having @Test annotation but the function with @BeforeClass will be execute only one time before all the test functions in the class. @Before注释函数将在具有@Test注释的类中的每个测试函数之前执行，而具有@BeforeClass的函数仅在类中的所有测试函数之前执行一次。

Similarly function with @After annotation will be executed after each of test function in the class having @Test annotation but the function with @AfterClass will be execute only one time after all the test functions in the class. 类似地，具有@After批注的函数将在类中具有@Test批注的每个测试函数之后执行，但是具有@AfterClass的函数仅在该类中的所有测试函数之后执行一次。

SampleClass 样本类

public class SampleClass {public String initializeData(){return "Initialize";}public String processDate(){return "Process";}}

SampleTest 样品测试

public class SampleTest {private SampleClass sampleClass;@BeforeClasspublic static void beforeClassFunction(){System.out.println("Before Class");}@Beforepublic void beforeFunction(){sampleClass=new SampleClass();System.out.println("Before Function");}@Afterpublic void afterFunction(){System.out.println("After Function");}@AfterClasspublic static void afterClassFunction(){System.out.println("After Class");}@Testpublic void initializeTest(){Assert.assertEquals("Initailization check", "Initialize", sampleClass.initializeData() );}@Testpublic void processTest(){Assert.assertEquals("Process check", "Process", sampleClass.processDate() );}}

Output 输出量

Before Class
Before Function
After Function
Before Function
After Function
After Class

In Junit 5 在Junit 5中

@Before = @BeforeEach
@BeforeClass = @BeforeAll
@After = @AfterEach
@AfterClass = @AfterAll

#5楼

import org.junit.Assert
import org.junit.Before
import org.junit.BeforeClass
import org.junit.Testclass FeatureTest {companion object {private lateinit var heavyFeature: HeavyFeature@BeforeClass@JvmStaticfun beforeHeavy() {heavyFeature = HeavyFeature()}}private lateinit var feature: Feature@Beforefun before() {feature = Feature()}@Testfun testCool() {Assert.assertTrue(heavyFeature.cool())Assert.assertTrue(feature.cool())}@Testfun testWow() {Assert.assertTrue(heavyFeature.wow())Assert.assertTrue(feature.wow())}
}

Same as 如同

import org.junit.Assert
import org.junit.Testclass FeatureTest {companion object {private val heavyFeature = HeavyFeature()}private val feature = Feature()@Testfun testCool() {Assert.assertTrue(heavyFeature.cool())Assert.assertTrue(feature.cool())}@Testfun testWow() {Assert.assertTrue(heavyFeature.wow())Assert.assertTrue(feature.wow())}
}

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@ Before，@ BeforeClass，@ BeforeEach和@BeforeAll之间的区别

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