How to generate session variables while testing with phpunit

One possible answer to your problem is "Dependency Injection", frankly the one i like best. Just plain mocking is also possible.

Some expamples

<?php 
// You could pass the session into the object while constructing it
// so in your test you can pass in a "fake" user object (see below)
class Some_model extends Model {
function Some_model($user_object) {
    $user_object->yourFunctions();
}

this way you don't have to rely on some global state beeing set up the right way.

If that doesn't work for you ( i don't know codeigniter really well ) you could maybe to it like this:

<?php 
class Some_model extends Model {
function Some_model($user_object=null) {
    if($user_obj === null) {
        $user_obj = @unserialize($this->db_session->userdata('user_object')); 
    }
    $user_object->yourFunctions();
}

so in your tests you pass in a mocked user object ( a fake instance you created, for mocking see the docs) and your normal code doesn't have to change.

Also a good read: Slides about PHPUnit best practices from the PHPUnit Author. Hopefully the help clarify what i was trying to explain :)

Edit

sidhartha asked for some help with the mocking so i wrote some more demo code. I've stripped out most things to provide a full executable example as i guess "code you can run" is more helpful then anything else.

Let's say this is the code you want to test (reduced to the userid so it's shorter)

<?php
class Some_model extends Model 
{

    var $userid;
    var $permisson_object;

    function Some_model()
    {
        parent::Model();
        $user_obj = @unserialize($this->db_session->userdata('user_object')); 
        //following line shows error
        $this->permisson_object = $user_obj->getPermissionObject();
        $this->userid = $user_obj->getUserid();
     }

 }

Working with what i have tried to explain you could build a test like this one (everything in one file to make copy paste eaiser, of course one would split it)

class Model { public function Model() {}  }

class Some_model extends Model
{

    var $userid;
    var $permisson_object;

    function Some_model($user_obj)
    {
        parent::Model();
        //following line shows error
        $this->userid = $user_obj->getUserid();
        $this->permisson_object = $user_obj->getPermissionObject();
     }

    public function getThatUserid() {
        // Just to show off how mocking works a little bit better :)
        return $this->userid;
    }

}

class Permissions {
    public function getPermissions() {
        // lots of code here maybe
        return array("something from" => "the database");
    }
}

class User {
    public function getUserid() {
        // code code
        return 1;
    }
    public function getPermissionObject() {

    }
}



class Some_modelTest extends PHPUnit_Framework_Testcase {

    public function testConstruction() {
        $mockUser = $this->getMock("User");
        $mockPermissions = $this->getMock("Permission");

        $mockUser->expects($this->once())
                 ->method("getUserid")
                 ->will($this->returnValue(100));
#        $mockPermissions->expects($this->once())
#                        ->method("getPermissions");

        // Now for the "magic"
        $mockUser->expects($this->once())
                 ->method("getPermissionObject")
                 ->will($this->returnValue($mockPermissions));
         // ^^ now we are all set and user_obj is independen of the permissons object
        // Now pass the "Fake" user into the model
        $model = new Some_model($mockUser);
        // and just to show off the "will return value stuff"
        $this->assertSame(100, $model->getThatUserid());
    }
}

phpunit Some_modelTest.php PHPUnit 3.4.15 by Sebastian Bergmann.

.

Time: 0 seconds, Memory: 4.25Mb

OK (1 test, 3 assertions)

I really hope that helps. It's a lot of code but as a demo it should work for you.