Laravel 5.0 model test Mockery unable to mock method/static method does not exist?

Question

I am using Laravel 5.0 to create phpunit test alongside the actual model. I get errors in phpunit tests but no errors when controller calls the model and it returned the desired data.

sample.php

<?php namespace App;
use Illuminate\Database\Eloquent\Model;


class sample extends Model  {


/**
* The database table used by the model.
*
* @var string
*/
protected $table = 'sample';

/**
* The attributes that are mass assignable.
*
* @var array
*/
protected $fillable = ['id','username','details','image'];

/**
* The attributes excluded from the model's JSON form.
*
* @var array
*/

public static function test()
{
    return "Returned Text.";
}
public static function gettest()
{
    return self::test();
}

public static function getItem()
{
    return self::orderBy('username','asc')->get();
}

public static function findItem($id)
{
    return self::find($id);
}

}

SampleTest.php

<?php namespace App;

use Mockery as m;

class SampleTest extends \PHPUnit_Framework_TestCase {

protected function setUp()
{
    $this->mock = m::mock('App\sample')->makePartial();
}

protected function tearDown()
{
    m::close(); 
}

/** @test */
public function should_return_string()
{
    $response = $this->mock->test();
    var_dump("test() returns :".$response);
}

/** @test */
public function should_return_string_from_test_function()
{
    $response = $this->mock->gettest();
    var_dump("gettest() returns :".$response);
}

/** @test */
public function should_return_mocked_data()
{
    $this->mock->shouldReceive('test')->andReturn('Return Mocked Data');
    $response = $this->mock->gettest();
    var_dump("gettest() returns :".$response);
}

/** @test */
public function should_return_some_data_using_this_mock()
{
    $this->mock->shouldReceive('get')->andReturn('hello');
    $response = $this->mock->getItem();
}

}

Problem When I use controller to call the model, it returned the desired data. When I run phpunit on command prompt:-

1. test function is not mocked properly as it still returns the original string

2. getItem and findItem functions return an error saying

   1) App\SampleTest::should_return_some_data_using_this_mock BadMethodCallException: Static method Mockery_0_App_sample::getItem() does not exist on this mock object

Question How can I mock the function properly? Why it is saying the error code as shown above? Where was I doing it wrong?

Any help will be much appreciated.

Note: Test assertions is removed and replaced with var_dump to see the output on the command prompt.