That is my methodology, for which I need to write a unit check:

personal $productRepository;

public operate __construct(
    ProductRepositoryInterface $productRepository
)
{
    $this->productRepository = $productRepository;
}

public operate getProductName(int $productEntityId) : string
{
    $myProduct = $this->productRepository->getById($productEntityId);
    return (string) $myProduct->getName();
}

and my check:

/**
 * @dataProvider productEntityIds
 * @param $productEntityId
 */
public operate testGetProductName($productEntityId)
{
    $this->assertInternalType('string', $this->myCustomClass->getProductName($productEntityId));
    //assertIsString().
}

public operate productEntityIds()
{
    return [
        [1]
        [2],
        [3],
        [5],
        ['myString']
    ];
}

Once I run my check, I’m receiving the next error message:
Error: Name to a member operate getName() on null

If I name the tactic( getProductName() ), in a cronjob or an observer I efficiently acquired the product title. However If name it from the phpunit check , I’m receiving that error. Does anybody know why ?

Thanks