Failure to properly load model inside model as a fixture

Function.php

	public function lastUpdated($id) {

		//Set up new Shift model only if not already set (fixes problems with testing)
		if(!$this->Shift) {
			App::uses('Shift', 'Model');
			$this->Shift = new Shift();
		}
		$calendar = $this->findById($id, array(
				'start_date', 'end_date'));
		$lastUpdated = $this->Shift->find('all', array(
				'fields' => array('Shift.updated', 'Shift.date'),
				'conditions' => array(
						'Shift.date >=' => $calendar['Calendar']['start_date'],
						'Shift.date <=' => $calendar['Calendar']['end_date'],
				),
				'order' => array(
						'Shift.updated' => 'DESC',
				)
		));
		return $lastUpdated['Shift']['updated'];
	}

Test.php

	public function testLastUpdated () {
		App::uses('Shift', 'Model');

		$this->Shift = ClassRegistry::init('Shift');

		$result = $this->Calendar->lastUpdated('1');
		debug($result);
		$expected = array(
				'start_date' => '2011-12-01',
				'end_date' => '2011-12-22'
		);

		//TODO: EXPECTED FAIL DUE TO nested model call.
		$this->assertEquals($expected, $result);
		}