JUnit assertFalse example

Junit 5’s org.junit.jupiter.Assertions class provides different static assertions method to write test cases.

Assertions.AssertFalse() checks if supplied boolean condition is false. In case, condition is true, it will through AssertError.

Here is simple example

package org.arpit.java2blog;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

public class AssertFalseTest {

	AssertFalseTest att;

    public boolean isPalindrome(String str)
	{
		for (int i = 0,j=str.length()-1; i <str.length()/2; i++,j--) {

			if(str.charAt(i)!=str.charAt(j))
			{
				return false;
			}

		}
		return true;
	}

	@BeforeEach
	public void beforeEachTest()
	{
		att = new AssertFalseTest();
	}

	//assertFalse(boolean condition)
	@Test
	public void palindormeTestwithCondition(){
		Assertions.assertFalse(att.isPalindrome("ADAM"));
	}

	// assertFalse(boolean condition, String message)
	@Test
	public void palindormeTestwithConditionAndMessage(){
		Assertions.assertFalse(att.isPalindrome("MADAM"),"String is palindrome");
	}

	// assertFalse(BooleanSupplier booleanSupplier)
	@Test
	public void palindormeTestWithBooleanSupplier(){
		Assertions.assertFalse(() -> att.isPalindrome("ASDAS"));
	}

	// 	assertFalse(boolean condition, Supplier<String> messageSupplier)
	@Test
	public void palindormeTestWithConditionAndSupplier(){
		Assertions.assertFalse(att.isPalindrome("LEVEL"),() -> "String is palindrome");
	}

	// assertFalse(BooleanSupplier booleanSupplier, String message)
	@Test
	public void palindormeTestWithBooleanSupplierAndMessage(){
		Assertions.assertFalse(() -> att.isPalindrome("PLAN"),"String is palindrome");
	}

	// assertFalse(BooleanSupplier booleanSupplier, Supplier<String> messageSupplier)
	@Test
	public void palindormeTestWithBooleanSupplierAndSupplier(){
		Assertions.assertFalse(() -> att.isPalindrome("RADAR"),() -> "String is palindrome");
	}
}

When you run above testcase, you will get below output:

Let’s understand output of each testcase:

palindormeTestwithCondition – Pass

As “ADAM” is not palindrome, so this testcase will pass.

palindormeTestwithConditionAndMessage – Fail

As “MADAM” is palindrome, so this testcase will fail.

palindormeTestWithBooleanSupplier – Pass

As “ASDAS” is not palindrome, so this testcase will pass.

palindormeTestWithConditionAndSupplier – Fail

As “LEVEL” is palindrome, so this testcase will fail.

palindormeTestWithBooleanSupplierAndMessage – Pass

As “PLAN” is not palindrome, so this testcase will pass.

palindormeTestWithBooleanSupplierAndSupplier – Fail

As “RADAR” is palindrome, so this testcase will fail.

That’s all about Assertions.assertFalse()