test_for_gabor.php

<?php

namespace Drupal\Tests\Core;

use Drupal\Tests\UnitTestCase;

class SomeClass {
  function someMethod() {
    $executable = \Drupal\views\Views::executableFactory();
    $item = $executable->getItem('somedisplayid', 'sometype', 'someid');
    if ($item === NULL) {
      return 'wtf!';
    }
  }
}

class SomeTest extends UnitTestCase {

  function testSomething() {
    $mock_exec = $this->getMockBuilder('Drupal\views\ViewExecutable')
      ->disableOriginalConstructor()
      ->getMock();
    $mock_exec->expects($this->any())
      ->method('getItem')
      ->will($this->returnCallback(function() {
        return NULL;
      }));

    $container = $this->getMock('Symfony\Component\DependencyInjection\ContainerInterface');
    $container->expects($this->any())
      ->method('get')
      ->with($this->equalTo('views.executable'))
      ->will($this->returnCallback(function() use ($mock_exec) {return $mock_exec;}));

    \Drupal::setContainer($container);

    $someclass = new Someclass;
    $this->assertEquals('wtf!', $someclass->someMethod());
  }
}