Magento - UnitTests - Mock Objects

I am writing some tests for a Magento module, using Ivan Chepurnyi's extension, and I'm having trouble using the mock objects.

Here is the class:

<?php
class Namespace_Module_Block_Class extends Mage_Core_B开发者_高级运维lock_Template
{
    private $_salesCollection;

    public function __construct()
    {
        $this->_salesCollection = Mage::getModel('module/classA')->getCollection()
                                ->addFieldToFilter('id', $this->_getId());
    }

    public function _getId()
    {
        return Mage::getModel('module/classB')->getId();//session params
    }

    public function getSalesTotalNumber()
    {
        return $this->_salesCollection->count();
    }
}

The method I'm trying to test is getSalesTotalNumber().

And here is the test:

<?php
class Namespace_Module_Test_Block_Class extends EcomDev_PHPUnit_Test_Case
{
    private $_mock;

    public function setUp()
    {
        $this->_mock = $this->getMock('Namespace_Module_Block_Class',
                                        array('_getId')
                                      );
        $this->_mock->expects($this->any())
                    ->method('_getId')
                    ->will($this->returnValue(1024));

        parent::setUp();
    }

    /**
     * @test
     * @loadFixture
     * @loadExpectation
     */
    public function testSalesTotalNumber()
    {
        $actual = $this->_mock->getSalesTotalValue();
        $expected = $this->_getExpectations()->getSalesTotalNumber();

        $this->assertEquals($expected, $actual);
    }
}

As you can see, what I want to do is overwrite the _getId() method so that it returns an id which match the id in the fixture and so load the collection. But it doesn't work :-(.

In my test, if I echo $this->_mock->_getId() it returns the correct Id (1024). But in the __construct() of my class $this->_getId() returns null, which is the expected value during testing (I mean, during testing there is no session, so it can't get the object's Id as I store it in a session variable). So the _getId() method isn't mocked by my test case.

Any help will be highly appreciated.

So my problem was not in the mock/test but in the class.
I have moved the content of __construct() into a protected method which returns the collection object. That's how my class looks like now:

<?php
class Namespace_Module_Block_Class extends Mage_Core_Block_Template
{
    private $_salesCollection;

    protected function _getAffiliateSales()
    {
        if (is_null($this->_salesCollection)) {
            $affiliateId = $this->_getId();
            $this->_salesCollection = Mage::getModel('module/classA')
                                ->addFieldToFilter('id', $affiliateId);
        }
        return $this->_salesCollection;
    }

    public function _getId()
    {
        return Mage::getModel('module/classB')->getId();//session params
    }

    public function getSalesTotalNumber()
    {
        return $this->_getAffiliateSales()->count();
    }
}