@Before的代碼在每次測試之前執行

@BeforeClass在整個測試方法執行之前運行一次

如果您的測試類有十個測試，則@Before代碼將執行十次，但是@BeforeClass將僅執行一次。

當多個測試需要共享相同的代碼時，可以使用@BeforeClass 。 建立數據庫連接屬于此類。

您可以將代碼從@BeforeClass移到@Before ，但是您的測試運行可能需要更長的時間。

注意，標記為@BeforeClass的代碼作為靜態初始化程序運行，因此它將在創建測試夾具的類實例之前運行。

在JUnit 5中 ，標簽@BeforeEach和@BeforeAll與JUnit 4中的@Before和@BeforeClass等效。

它們的名稱更能說明它們的運行時間，可以解釋為：“在所有測試之前執行一次”和“每次測試之前執行”。?

Junit4和Junit5中每個注釋之間的區別：

+-------------------------------------------------------------------------------------------------------+
|                                       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.                        |              |             |
+-------------------------------------------------------------------------------------------------------+

?兩個版本中的大多數注釋都相同，但幾乎沒有區別

執行順序

?

@Before注釋函數將在具有@Test注釋的類中的每個測試函數之前執行

@BeforeClass注釋函數僅在類中的所有測試函數之前執行一次

@After注釋函數將在類中具有@Test批注的每個測試函數之后執行

@AfterClass注釋函數僅在該類中的所有測試函數之后執行一次

類

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

測試

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() );}}

輸出

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.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())}
}

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())}
}