Test for https://github.com/dnadesign/silverstripe-elemental/issues/220

Elemental220Test.php

<?php

use DNADesign\Elemental\Extensions\ElementalPageExtension;
use DNADesign\Elemental\Models\ElementalArea;
use Elemental220Test\StubBlock;
use Elemental220Test\StubExtension;
use Elemental220Test\StubPage;
use SilverStripe\Dev\SapphireTest;

class Elemental220Test extends SapphireTest
{
    protected static $required_extensions = [
        StubPage::class => [
            ElementalPageExtension::class,
        ],
        // This extension should prove the bug - comment the following 3 lines out and tests pass
        ElementalArea::class => [
            StubExtension::class,
        ],
    ];

    protected static $extra_dataobjects = [
        StubPage::class,
        StubBlock::class,
    ];

    protected $usesDatabase = true;

    public function testDuplicationBug()
    {
        // Create a page and elemental area
        $page = new StubPage();
        $page->Title = 'Test Page';
        $page->write();

        $this->assertNotEmpty($page->ElementalAreaID, 'Page is assigned an elemental area on write');

        // Create two blocks and assign them to the elemental area for the page
        $block1 = new StubBlock();
        $block1->ParentID = $page->ElementalAreaID;
        $block1->write();

        $block2 = new StubBlock();
        $block2->ParentID = $page->ElementalAreaID;
        $block2->write();

        $this->assertCount(2, $page->ElementalArea()->Elements(), 'Page has two blocks');

        // Duplicate the page
        $page2 = $page->duplicate();

        $this->assertNotEmpty($page2->ElementalAreaID, 'Duplicated page has an elemental area');
        $this->assertNotEquals($page->ElementalAreaID, $page2->ElementalAreaID, 'Elemental areas are different');
        $this->assertCount(2, $page2->ElementalArea()->Elements(), 'Duplicated page has blocks');
        $this->assertNotEquals(
            $page->ElementalArea()->Elements()->column('ID'),
            $page2->ElementalArea()->Elements()->column('ID'),
            'Blocks are different instances'
        );


    }
}

StubBlock.php

<?php

namespace Elemental220Test;

use DNADesign\Elemental\Models\BaseElement;
use SilverStripe\Dev\TestOnly;

class StubBlock extends BaseElement implements TestOnly
{

}

StubExtension.php

<?php

namespace Elemental220Test;

use SilverStripe\ORM\DataExtension;

class StubExtension extends DataExtension
{
    /**
     * This config is already defined on BaseElement - applying it with an extension as well
     * results in duplication happening twice
     */
    private static $cascade_duplicates = ['Elements'];
}

StubPage.php

<?php

namespace Elemental220Test;

use Page;
use SilverStripe\Dev\TestOnly;

class StubPage extends Page implements TestOnly
{

}