Detailed explanation of JUnit unit test framework

Recommended reading ：Java Custom annotation

Junit summary

unit testing
Unit testing is to write test code for the smallest functional unit ,Java The smallest functional unit of a program is a method , therefore , Unit testing is for Java Method testing , Then check the correctness of the method .

The disadvantages of manual testing
only one main Method , If the test of a method fails , Other methods of testing will be affected . Unable to get the test result report , The programmer needs to observe whether the test is successful . Unable to automate testing .

Junit Unit test framework
JUnit It's using Java Language implementation of unit testing framework , It's open source ,Java Developers should learn and use JUnit Write unit tests ; Besides , Almost all IDE Tools are integrated JUnit, So that we can go straight to IDE Write and run JUnit test .

JUnit advantage
1.JUnit You can flexibly choose which test methods to perform , The test method can be executed with one key ;
2.Junit You can generate test reports for all methods ;
3. A method test in the unit test failed ( As abnormal ), Tests that do not affect other test methods ;

Quick start

Usage flow

1. take JUnit Of jar Package import into project
   a. IDEA Usually integrated Junit frame , Generally, there is no need to import ;
   b. If IDEA Not integrated well , You need to manually import the following 2 individual JUnit Of jar Package to module ;
   
2. Write test methods ： The test method must be a public non static method with no parameters and no return value ;
3. Use... On test methods @Test annotation ： Note that this method is a test method ;
4. Complete the expected correctness test of the tested method in the test method ;
5. Check the test method , choice “JUnit function ” , If the test is good, it is green ; If the test fails , It's red ;

To test a method, right-click the method to start the test , Test all methods , You can choose classes or modules to start .

Be careful
The defined test method must be parameterless and return value , And open methods .

Common notes for unit testing

Junit 4.xxxx edition

annotation	explain
@Test	The test method
@Before	Used to modify instance methods , This method is executed once before each test method is executed
@After	Used to modify instance methods , This method will be executed once after each test method execution
@BeforeClass	Used to statically decorate methods , This method will be executed only once before all test methods
@AfterClass	Used to statically decorate methods , This method will be executed only once after all test methods

Junit 5.xxxx edition

annotation	explain
@Test	The test method
@BeforeEach	Used to modify instance methods , This method is executed once before each test method is executed
@AfterEach	Used to modify instance methods , This method will be executed once after each test method execution
@BeforeAll	Used to statically decorate methods , This method will be executed only once before all test methods
@AfterAll	Used to statically decorate methods , This method will be executed only once after all test methods

Code example

public class TestUserService {
    

    //  Modify the instance method 
    @Before
    public void before(){
    
        System.out.println("===before Method executes once ===");
    }

    @After
    public void after(){
    
        System.out.println("===after Method executes once ===");
    }

    //  Modified static method 
    @BeforeClass
    public static void beforeClass(){
    
        System.out.println("===beforeClass Method executes once ===");
    }

    @AfterClass
    public static void afterClass(){
    
        System.out.println("===afterClass Method executes once ===");
    }


    /**  The test method   Be careful ： 1、 Must be public , No parameter   Methods with no return value  2、 The test method must use @Test Comment mark . */
    @Test
    public void testLoginName(){
    
        UserService userService = new UserService();
        String rs = userService.loginName("admin","123456");

        //  Test the correctness of the expected results ： Assertion .
        Assert.assertEquals(" There may be a problem with your login business ", " Login successful ", rs );
    }

    @Test
    public void testSelectNames(){
    
        UserService userService = new UserService();
        userService.selectNames();
    }

}


public class UserService {
    
    public String loginName(String loginName , String passWord){
    
        if("admin".equals(loginName) && "123456".equals(passWord)){
    
            return " Login successful ";
        }else {
    
            return " There is a problem with the user name or password ";
        }
    }

    public void selectNames(){
    
        System.out.println(10/2);
        System.out.println(" Query all user names succeeded ~~");
    }
}