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Java Unit Testing with JUnit 5

Using assertNull() and assertNotNull() methods together

Explore how to apply assertNull and assertNotNull methods in JUnit 5 to test different return values from Java methods. Understand how to verify null, empty, and non-null strings in unit tests to ensure accurate test coverage.

We'll cover the following...

Demo

Step 1 - Create a Java class in Eclipse as discussed in previous lessons.

Step 2 - Give it a name as, StringUtils.`

Java
package com.hubberspot.junit5.assertions;
public class StringUtils {
	
	public static String reverse(String input) {
		if(input == null) {
			return null;
		}
		
		if(input.length() == 0) {
			return "";
		}
		
		char[] charArray = input.toCharArray();
		int start = 0;
		int end = input.length() - 1;
		
		while(start < end) {
			char temp = charArray[start];
			charArray[start] = charArray[end];
			charArray[end] = temp;
			start++;
			end--;
		}
		
		return new String(charArray);
	}
	
}

Class Under Test - StringUtils

StringUtils is our class under test. It has one method as, reverse(). This method takes in a String and returns reverse of it.

For example -

  1. If we provide input String as, “ABCD”, it returns back “DCBA”.

  2. If we provide input String as, “Student”, it returns back “tnedutS”.

  3. If we provide input ...