Example of a very basic unit test in PHP

code.php

<?php 

function sum( $number1, $number2 )
{
	if( ! is_int( $number1 ) || ! is_int( $number2 ) )
		throw new Exception( 'Both arguments should be numeric' );
		
	return $number1 + $number2;
}

test.php

<?php

include "code.php";

class CodeTest extends PHPUnit_Framework_TestCase
{

	public function testValidSum()
	{
		$result = sum( 4, 5 );
		$this->assertEquals( 9, $result );
	}

	public function testNegativeIntSum()
	{
		$result = sum( -8, 10 );
		$this->assertEquals( 2, $result );
	}

	/**
	 * @expectedException Exception
	 */
	public function testInvalidInput()
	{
		$result = sum( "4", 5);
	}

}