Fake Test Double Using Prophecy
Fake test double is a simplified version of a dependency. A good example is an in memory or file system repository in exchange for database repository. Fake objects implement the interface of dependency.
Below is the class which has a constructor dependency:
<?php
namespace App;
class Questioner
{
/** @var OutputInterface */
private $output;
public function __construct(OutputInterface $output)
{
$this->output = $output;
}
}
The OutputInterface is:
<?php
namespace App;
interface OutputInterface
{
/**
* Save the data.
*
* @param array $data
* @param string $name
* @return boolean
*/
public function save(array $data, $name = null);
}
In production you would like to use a database output for persistence. The following object might be used:
<?php
namespace App;
class DatabaseOutput implements OutputInterface
{
/** @inheritDoc */
public function save(array $data, $name = null)
{
// call database or do other time consuming tasks
}
}
This will make unit testing impossible. To test the code you would need to use functional tests which would require a database. Code using the database will run much longer and the longer tests run the higher the chance they won't be run at all.
For this reason in unit testing a simpler version of dependency can be used:
<?php
namespace App;
class InMemoryOutput implements OutputInterface
{
/** @inheritDoc */
public function save(array $data, $name = null)
{
// simple, fast implementation for testing
}
}
This article is from the Test doubles using Prophecy series which is made from following articles: