JUnit 4 Tutorial

In this post, we will demonstrate how to use Assert.fail() method with an example.

The fail() method belongs to JUnit 4 org.junit.Assert class.

The fail assertion fails a test throwing an AssertionError. It can be used to verify that an actual exception is thrown or when we want to make a test failing during its development.

Check out JUnit 5 tutorials and examples at https://www.javaguides.net/p/junit-5.html

In JUnit 5 all JUnit 4 assertion methods are moved to org.junit.jupiter.api.Assertions class.

void org.junit.Assert.fail(String message)

Fails a test with the given message.

Parameters:

message the identifying message for the AssertionError (null okay)

Assert.fail(String message) Method Example

Let's first create the largest(final int[] list) method to find the largest number in an array:

import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;

public class AssertFailExample {

 public int largest(final int[] list) {
      int index, max = Integer.MAX_VALUE;
      for (index = 0; index < list.length - 1; index++) {
         if (list[index] > max) {
             max = list[index];
         }
      }
      return max;
 }

Let's write the JUnit test for above largest(final int[] list) method:

@Test
 public void testEmpty() {
     try {
         largest(new int[] {});
         fail("Should have thrown an exception");
     } catch (final RuntimeException e) {
         assertTrue(true);
     }
   } 
}

Output:

Related JUnit Examples

JUnit Assert.assertArrayEquals() Method Example
JUnit Assert.assertEquals() Method Example
JUnit Assert.assertTrue() Method Example
JUnit Assert.assertFalse() Method Example
JUnit Assert.assertNull() Method Example
JUnit Assert.assertNotNull() Method Example
JUnit Assert.assertSame() Method Example
JUnit Assert.assertNotSame() Method Example
JUnit Assert.fail() Method Example