test dependencies example

test_dependencies.php

<?php
class Item_handler {

  public static function upload_one() {
    // Do something expensive with lots of deps
    return true;
  }

  public function upload_two() {
    // Do something expensive with lots of deps
    return true;
  }

}

class Filter_handler {
  public function __construct( $item_handler = null ) {
    $this->item_handler = $item_handler;
  }

  public function handle_new_avatar() {
    // This is a hard dependency on Item_handler
    return Item_handler::upload_one();
  }


  public function handle_new_avatar_testable() {
    return $this->item_handler->upload_two(); 
  }
}

// Tests

class Mock_Item_Handler() {
  public function __construct( $data ) {
    $this->data = $data;
  }

  public function upload_two() {
    return $this->data;
  }
}

class Filter_handler_Test() extends Test_Case {
  public function test_upload() {

    // Since handle_new_avatar() has a hard dependency on Item_handler, this test will
    // also execute code in Item_handler::upload_one() and becomes dependant on any set up
    // requirements it may have.
    $filter_handler = new Filter_handler();
    $this->assertTrue( $filter_handler->handle_new_avatar() );


    // Testing Filter_handler::handle_new_avatar_testable() is easier because we can inject a mock object
    // that allows us to focus on the logic in the function under test rather than worrying about 
    // its depdencencies.
    //
    // Chain of dependencies is broken. Testing the Item_handler class isn't affected much by prefering instance
    // methods over static ones, but testing anything that uses the Item_handler is made easier.
    $mock_return_data = true;
    $mock = new Mock_Item_Handler( $mock_return_data );
    $filter_handler = new Filter_handler( $mock );

    $this->assertTrue( $filter_handler->handle_new_avatar_testable() );

    $mock_return_data = false;
    $mock = new Mock_Item_Handler( $mock_return_data );
    $filter_handler = new Filter_handler( $mock );

    $this->assertFalse( $filter_handler->handle_new_avatar_testable() );

  }
}