"Monadic" Models for improved unit-testability. (Pure - Impure separation of control)

ImpureDatabaseWrapper.php

<?php
class ImpureDatabaseWrapper {

    private $sql;
    private $pureBinding;

    /**
    * @var \Zend_Db_Select $sql
    * @var \Closure $pureBinding (Closure that contains "pure" code - i.e. it doesn't cause any side-effects!)
    */
    public function __construct( \Zend_Db_Select $sql, \Closure $pureBinding ) 
    {
        $this->sql = $sql;
        $this->pureBinding = $pureBinding
    }

    /**
    * @return mixed
    */
    public function get()
    {
        $result = $sql->query()->fetchAll()
        $closure = $this->pureBinding;
        
        return $closure( $result );
    }
    
    /**
    * Call this in unit tests
    * 
    * @return \Closure
    */
    public function getBinding()
    {
        return $this->pureBinding
    }

}

Model_SomeDatabase.php

<?php
class Model_SomeDatabase {


    public function retrieveName( $id ) {
        
        /* Assume ::getInstance is a factory method for a Zend_Db_Table concrete class */
        /* @var $table \Zend_Db_Table_Abstract */
        $table = Table::getInstance()
        
        $select = $table->select();
        $select->where('id = ?', $id);
        
        return new ImpureDatabaseWrapper( $select, function( $result ) {
            //Naive example (but assume complex manipulation here)
            return $result['first_name'] . ' ' . $result['last_name']
        } );
        
            
    }

}

TestSomeDatabase.php

<?php
class TestSomeDatabase extends PHPUnit_TestCase {

    public function testRetrieveName() {
        //We don't need to test Zend_Db, but we do want to test that the names are concatentated correctly
        $model = new Model_SomeDatabase();
        $pureLogic = $model->retrieveName()->getBinding();
        
        $array = array(
            'first_name' => 'a',
            'last_name'  => 'b'
        );
        
        /* This is a naive test, but assume that this is testing some really complex pure manipulation is correct */
        $this->assertEqual( 'a b', $pureLogic( $array ) );
        
    }

}