Setting $_POST, Getting with input->post

[eluser]jlester[/eluser]
I am writing a test suite for an application and have model functions that look like:

Code:

function model_function() {
    $var1 = $this->input->post('var1');
    $var2 = $this->input->post('var2');
    ...
}

What I would like to do (and what I have tried) is to write a test function that looks like this:

Code:

function test_controller() {
    $this->load->model('my_model');
    $_POST['var1'] = 'value1';
    $_POST['var2'] = 'value2';
    $ret = $this->my_model->model_function();
    $this->_assert_true($ret);
}

So, in words, I'd like to populate the $_POST variable then call a model function that will read the values in $_POST using $this->input->post(). This however does not seem to work. input->post() returns FALSE for everything.

Is this a case where CI is setting an internal variable when it is initialized and used by input->post() such that setting $_POST values after CI has initialized is pointless? If this is not the case, what am I missing? It seems like my approach ought to work.

Thank you.