JUNIT 5的org.junit.jupiter.Assertions类提供了不同的静态断言方法来编写测试用例。

请注意，在JUnit 4或者JUnit 3的情况下，我们需要使用JUnit的Org.Junit.Assert类来使用AssertNotnull方法来声明。

assertions.assertnotnull()检查对象是否没有null。
如果，对象是null，它将通过asserterror。

public static void assertNotNull(Object actual)
public static void assertNotNull(Object actual, String message)
public static void assertNotNull(Object actual, Supplier messageSupplier)

这是一个简单的例子

package org.igi.theitroad;
 
import java.util.HashMap;
import java.util.Map;
 
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
 
public class AssertNotNullTest {
	
	AssertNotNullTest annt;
 
    public String getCapital(String country){
        Map<String,String> countryCapitalMap = new HashMap<String,String>();
        countryCapitalMap.put("Netherlands", "Delhi");
        countryCapitalMap.put("Nepal", "Kathmandu");
        countryCapitalMap.put("China", "Beijing");
        countryCapitalMap.put("Bhutan", "Thimphu");
        return countryCapitalMap.get(country);
    }
    
    @BeforeEach
	public void beforeEachTest()
	{
    	annt = new AssertNotNullTest();
	}
    /*
     * Examples for each overloaded methods of assertNotNull
     */
    
    //public static void assertNotNull(Object actual)
    @Test
    public void testNetherlands(){
    	String capitalNetherlands=annt.getCapital("Netherlands");
    	Assertions.assertNotNull(capitalNetherlands);
    }
    
    //public static void assertNotNull(Object actual, String message)
    @Test
    public void testUSA(){
    	String capitalUSA=annt.getCapital("USA");
    	//You can pass message as well
    	Assertions.assertNotNull(capitalUSA,"Capital should not be null");
    }
    
    //public static void assertNotNull(Object actual, Supplier messageSupplier)
    @Test
    public void testBhutan(){
    	String capitalUSA=annt.getCapital("Bhutan");
    	//You can pass message as well
    	Assertions.assertNotNull(capitalUSA,() -> "Capital should not be null");
    }
}