Zend framework PhpUnit test error due to calling a member function on null

So there are a few things I notice here:

1: You have not shown any code showing how you have hooked up your service to the service manager, so it is unclear if this will ever work

2: You directly instantiate your class when you need to be using the service manager grabber you have written

$this->serviceprovider = new ServiceProvider() ;

becomes

$serviceManagerGrabber   = new ServiceManagerGrabber();
$this->serviceManager = $serviceManagerGrabber->getServiceManager();
$this->serviceprovider = $this->serviceManager->get('YOUR_SERVICE_KEY');

3: You probably should start with unit tests not these module integration tests being explained in that article. see https://framework.zend.com/manual/2.3/en/modules/zend.test.phpunit.html

4: The ServiceLocatorAwareInterface is deprecated you should probably use a factory and the factories key of service manager config to inject your dependencies

5: Your code seems to mix doctrine and zend db I don't know why you've done this, but my suggestion is ... it's be a bad idea

Here is an example of how you might put this together:

module.config.php

<?php
namespace Application;

return [
'service_manager' => [
    'factories' => [
        'ServiceProvider' => function ($serviceManager) {
            // This shouldn't be in this anon function, it should be its own
            // factory but I'm lazy and already writing loads of code for this example
            // @see https://framework.zend.com/manual/2.4/en/in-depth-guide/services-and-servicemanager.html#writing-a-factory-class
            $service = new \Application\Service\ServiceProvider(
                $serviceManager->get('doctrine.entitymanager.orm_default')
            );

            return $service;
        },
    ]
],
];

ServiceProvider.php

<?php
namespace Application\Service;

use Doctrine\ORM\EntityManager;

class ServiceProvider
{
    protected $entityManager;

    public function __construct(EntityManager $entityManager)
    {
        $this->entityManager = $entityManager;
    }

    public function getModel()
    {
        return $this->entityManager- >getRepository('User\Entity\ServiceProvider');
    }

    public function getDetails($data = null, $fields='*')
    {
        $serviceProviderRepository = $this->entityManager->getRepository('User\Entity\ServiceProvider');

        return $data;
    }
}

ModuleTest

<?php
namespace ModulesTests\Application\Service;

use PHPUnit_Framework_TestCase;
use ModulesTests\ServiceManagerGrabber;

class ServiceProvidersTest extends PHPUnit_Framework_TestCase
{
    protected $serviceManager;
    protected $serviceprovider;

    public function setUp()
    {
        $serviceManagerGrabber   = new ServiceManagerGrabber();
       $this->serviceManager = $serviceManagerGrabber->getServiceManager();
        $this->serviceprovider = $this->serviceManager->get('ServiceProvider');
    }

    public function testSPdetails()
    {
        $stack = array('1','2');
        $this->serviceprovider->getDetails($stack);
    }
}

unit test:

<?php
namespace ModulesTests\Application\Service;

use PHPUnit_Framework_TestCase;
use Application\Service\ServiceProvider;
use Prophecy\Argument;

class ServiceProvidersUnitTest extends PHPUnit_Framework_TestCase
{
    protected $entityManager;
    protected $serviceprovider;

    public function setUp()
    {
        $this->entityManager = $this->prophesize("Doctrine\\ORM\\EntityManager");
        $this->entityManager->getRepository(Argument::exact('User\Entity\ServiceProvider'))
                        ->willReturn(true);
        $this->serviceprovider = new ServiceProvider($this->entityManager->reveal());
}

    public function testSPdetails()
    {
        $stack = array('1','2');
        $this->serviceprovider->getDetails($stack);
        $this->entityManager->getRepository(Argument::exact('User\Entity\ServiceProvider'))
                        ->shouldHaveBeenCalledTimes(1);
    }
}