Assertion mechanism in test class

Assertion （assertions）： Assertion （assertions） Is the core part of the test method , It is used to verify the conditions that the test needs to meet . These assertion methods are org.junit.jupiter.api.Assertions Static method of .JUnit 5 Built in assertions can be divided into the following categories ：
Check whether the data returned by the business logic is reasonable .
After all the test runs , There will be a detailed test report ;

1、 Simple assertion
Used for simple validation of a single value . Such as ：
Method explain
assertEquals Determine whether two objects or two primitive types are equal
assertNotEquals Determine whether two objects or two primitive types are not equal
assertSame Determine whether two object references point to the same object
assertNotSame Judge whether two object references point to different objects
assertTrue Determines whether the given Boolean value is true
assertFalse Determines whether the given Boolean value is false
assertNull Determine whether the given object reference is null
assertNotNull Determine whether the given object reference is not null

Code implementation ：

@Test
@DisplayName("simple assertion")
public void simple() {
    
     assertEquals(3, 1 + 2, "simple math");
     assertNotEquals(3, 1 + 1);

     assertNotSame(new Object(), new Object());
     Object obj = new Object();
     assertSame(obj, obj);

     assertFalse(1 > 2);
     assertTrue(1 < 2);

     assertNull(null);
     assertNotNull(new Object());
}

2、 Array assertion
adopt assertArrayEquals Method to determine whether two objects or arrays of primitive types are equal

@Test
@DisplayName("array assertion")
public void array() {
    
 assertArrayEquals(new int[]{
    1, 2}, new int[] {
    1, 2});
}

3、 Combine assertions
assertAll Method accepts multiple org.junit.jupiter.api.Executable An instance of a functional interface as an assertion to verify , Can pass lambda Expressions can easily provide these assertions

@Test
@DisplayName("assert all")
public void all() {
    
 assertAll("Math",
    () -> assertEquals(2, 1 + 1),
    () -> assertTrue(1 > 0)
 );
}

4、 Exception assertion
stay JUnit4 period , When you want to test the exception of a method , Need to use @Rule Annotated ExpectedException Variables are still troublesome . and JUnit5 Provides a new assertion method Assertions.assertThrows() , It can be used with functional programming .

@Test
@DisplayName(" Abnormal test ")
public void exceptionTest() {
    
    ArithmeticException exception = Assertions.assertThrows(
           // Throw assertion exception 
            ArithmeticException.class, () -> System.out.println(1 % 0));

}

5、 Assertion timeout
Junit5 It also provides Assertions.assertTimeout() Set timeout for test method

@Test
@DisplayName(" Timeout tests ")
public void timeoutTest() {
    
    // If the test method takes longer than 1s Will be abnormal 
    Assertions.assertTimeout(Duration.ofMillis(1000), () -> Thread.sleep(500));
}

6、 Fast failure 

adopt fail Method directly causes the test to fail

@Test
@DisplayName("fail")
public void shouldFail() {
    
 fail("This should fail");
}

Assertion is a very important function in our development , In development, we usually write the business logic module before going online , We have to write a unit test class for unit testing . It will give us a complete summary report , What became and what failed , It will give us an accurate positioning .

Use Maven Of test function , Only after the test is successful can we package