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

@Before的代码在每次测试之前执行

@BeforeClass在整个测试方法执行之前运行一次

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。

当多个测试需要共享相同的代码时，可以使用@BeforeClass 。 建立数据库连接属于此类。

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。

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。

在JUnit 5中 ，标签@BeforeEach和@BeforeAll与JUnit 4中的@Before和@BeforeClass等效。

它们的名称更能说明它们的运行时间，可以解释为：“在所有测试之前执行一次”和“每次测试之前执行”。 

Junit4和Junit5中每个注释之间的区别：

+-------------------------------------------------------------------------------------------------------+
¦                                       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.                        ¦              ¦             ¦
+-------------------------------------------------------------------------------------------------------+

 两个版本中的大多数注释都相同，但几乎没有区别

执行顺序

 

@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

@BeforeClass注释函数仅在类中的所有测试函数之前执行一次

@After注释函数将在类中具有@Test批注的每个测试函数之后执行

@AfterClass注释函数仅在该类中的所有测试函数之后执行一次

类

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

测试

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

输出

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

Junit 5中

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

 

import org.junit.Assert
import org.junit.Before
import org.junit.BeforeClass
import org.junit.Test
 
class FeatureTest {
    companion object {
        private lateinit var heavyFeature: HeavyFeature
        @BeforeClass
        @JvmStatic
        fun beforeHeavy() {
            heavyFeature = HeavyFeature()
        }
    }
 
    private lateinit var feature: Feature
 
    @Before
    fun before() {
        feature = Feature()
    }
 
    @Test
    fun testCool() {
        Assert.assertTrue(heavyFeature.cool())
        Assert.assertTrue(feature.cool())
    }
 
    @Test
    fun testWow() {
        Assert.assertTrue(heavyFeature.wow())
        Assert.assertTrue(feature.wow())
    }
}

如同

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