Difference between Before BeforeClass BeforeEach and BeforeAll

Question

What is the main difference between    Before and  BeforeClass   and in JUnit 5  BeforeEach and  BeforeAll   After and  AfterClass   According to the JUnit Api  Before is used in the following case      When writing tests  it is common to find that several tests need similar objects created before they can run     Whereas  BeforeClass can be used to establish a database connection  But couldn t  Before do the same

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The basic difference between all these annotations is as follows -

@BeforeEach - Use to run a common code before( eg setUp) each test method execution. analogous to JUnit 4’s @Before.
@AfterEach - Use to run a common code after( eg tearDown) each test method execution. analogous to JUnit 4’s @After.
@BeforeAll - Use to run once per class before any test execution. analogous to JUnit 4’s @BeforeClass.
@AfterAll - Use to run once per class after all test are executed. analogous to JUnit 4’s @AfterClass.

All these annotations along with the usage is defined on Codingeek - Junit5 Test Lifecycle

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The code marked  Before is executed before each test  while  BeforeClass runs once before the entire test fixture  If your test class has ten tests   Before code will be executed ten times  but  BeforeClass will be executed only once   In general  you use  BeforeClass when multiple tests need to share the same computationally expensive setup code  Establishing a database connection falls into this category  You can move code from  BeforeClass into  Before  but your test run may take longer  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   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

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Before and BeforeClass in JUnit  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   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   SampleClass  public class SampleClass       public String initializeData            return  Initialize              public String processDate            return  Process              SampleTest  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                 Output  Before Class Before Function After Function Before Function After Function After Class   In Junit 5    Before    BeforeEach  BeforeClass    BeforeAll  After    AfterEach  AfterClass    AfterAll

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Difference between each annotation  are     -------------------------------------------------------------------------------------------------------                                           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    Reference  Order of Execution   Dashed box -  optional annotation

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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              Same as  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

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Before JUnit4  - gt   BeforeEach JUnit5  - method is called before every test  After JUnit4  - gt   AfterEach JUnit5  - method is called after every test  BeforeClass JUnit4  - gt   BeforeAll JUnit5  - static method is called before executing all tests in this class  It can be a large task as starting server  read file  making db connection     AfterClass JUnit4  - gt   AfterAll JUnit5  - static method is called after executing all tests in this class

[java] Difference between @Before, @BeforeClass, @BeforeEach and @BeforeAll

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