FizzBuzz.php

<?php
class FizzBuzz {
  function toString($number) {
    $fizz[true] = "Fizz";
    $buzz[true] = "Buzz";
    $stillNumber[true] = $number;.

    $fizz[false] = $buzz[false] = $stillNumber[false] = ''; 

    $result = '';.
    $result .= $fizz[$number % 3 == 0];.
    $result .= $buzz[$number % 5 == 0];.
    $result .= $stillNumber[$number % 3 != 0 && $number % 5 != 0];.

    return $result;
  }
}

FizzBuzzTest.php

<?php
require_once 'FizzBuzz.php';

class FizzBuzzTest extends \PHPUnit_Framework_TestCase {
  private $fizzbuzz;

  function setUp() {
    $this->fizzbuzz = new FizzBuzz();
  }

  function testFizz() {
    $result = $this->fizzbuzz->toString(3);
    $this->assertEquals('Fizz', $result);
  }

  function testBuzz() {
    $result = $this->fizzbuzz->toString(5);
    $this->assertEquals('Buzz', $result);
  }

  function testFizzBuzz() {
    $result = $this->fizzbuzz->toString(15);
    $this->assertEquals('FizzBuzz', $result);
  }

  function testAnother() {
    $result = $this->fizzbuzz->toString(1);
    $this->assertEquals('1', $result);
  }
}