I have been tasked with writing a Unit Test for a method where I pass in a Node object, modify an Entity Reference field value, and then return a Node object.

Since this is a Unit test, I am unsure as to how to write an assertion.

Note: just included relevant code.

class ClassIAmTesting {     public function populateSymbols(Node $node) {        $node->field_symbols->appendItem(['target_id' => $symbol_id]);       return $node;     } } 

I have created a mock for the Entity Reference Field:

$entityReferenceMock = $this->getMockBuilder(EntityReferenceFieldItemList::class)       ->disableOriginalConstructor()       ->setMethods(['appendItem'])       ->getMock(); 

I have also created a mock of the Node Object

$nodeMock = $this->getMockBuilder(Node::class)       ->disableOriginalConstructor()       ->getMock();  $nodeMock->expects($this->any)       ->method('__get')       ->with('field_symbols_in_this_story')       ->willReturn($entityReferenceMock); 

The method returns a Node object but how can I assert that the Entity Reference Field Value has changed?

Edit: The class with more details:

class ClassIAmTesting {   public function populateSymbols(Node $node) {      $body = $node->field_body->value;      $dom = Html::load($body);     $xpath = new DOMXPath($dom);      foreach ($xpath->query('//span[@class="tooltip"]') as $xpathNode) {        $symbol_id = $xpathNode->getAttribute('data-symbol');        $node->field_symbols->appendItem(['target_id' => $symbol_id]);     }      return $node;   } }