Quicky PHPUnit accessiblity example.

gistfile1.php

<?php
/**
 * This class contains two private methods we wish to test.
 * In reality, it would also contain several public methods,
 * but that's immaterial to our discussion.
 * 
 * @package Tutorials
 */
class ClassToTest {
  /**
   * Does something cool
   * 
   * @returns string
   */
  private function someFunction() {
    return 'expected';
  } 
  
  /**
   * Filters an array
   * 
   * @param array $array
   * 
   * @returns array
   */
  private function someOtherFunction( $array ) {
    return array_filter( $array, 'remove_even_elements' );
  }
}

/**
 * The test class is using vanilla PHPUnit code and the standard
 * PHP reflection API.
 * 
 * @package Tutorials
 * @subpackage Tests
 */
class TestCase extends PHPUnit_Framework_TestCase {
  public function test_someFunction() {
    $instance = new ClassToTest();
    
    // Get a handle to the private method
    $someFunction = new ReflectionMethod(
      'ClassToTest',
      'someFunction'
    );
    $someFunction->setAccessible( true );
    
    $result = $someFunction->invoke( $instance );
    
    $this->assertEquals( 'expected', $result );
  }
  
  public function test_someOtherFunction() {
    $instance = new ClassToTest();
    
    // Get a handle to the private method
    $someFunction = new ReflectionMethod(
      'ClassToTest',
      'someOtherFunction'
    );
    $someOtherFunction->setAccessible( true );
    
    $initialArray = array( 1, 2, 3 );
    
    // Assume the filtering function removes any even members from the array.
    $filteredArray = $someOtherFunction->invoke( $instance, $initialArray );
    
    $this->assertEquals( 2, count( $filteredArray ) );
  }
}