Kernel Test: Error: Call to a member function get() on null

It's my first time with kernel tests.

I'm working with this test:

<?php

namespace Drupal\Tests\info_irpf_calculator\Kernel;

use Drupal\info_irpf_calculator\Model\IrpfUserData;
use Drupal\info_irpf_calculator\Model\IrpfUserDataInterface;
use Drupal\KernelTests\KernelTestBase;

/**
 * Tests the IRPF calculator.
 *
 * @group info_irpf_calculator
 *
 * @coversDefaultClass \Drupal\info_irpf_calculator\IrpfCalculator
 */
class IrpfCalculatorTest extends KernelTestBase {

  /**
   * {@inheritdoc}
   */
  public static $modules = ['info_irpf_calculator'];

  /**
   * The IRPF calculator service.
   *
   * @var \Drupal\info_irpf_calculator\IrpfCalculatorInterface
   */
  protected $irpfCalculator;

  /**
   * The IRPF specific values plugin manager.
   *
   * @var \Drupal\info_irpf_calculator\Plugin\IrpfSpecificValuesManagerInterface
   */
  protected $irpfSpecificValuesManager;

  /**
   * {@inheritdoc}
   */
  protected function setUp() {
    parent::setUp();

    $this->irpfCalculator = $this->container->get('info_irpf_calculator.calculator');
    $this->irpfSpecificValuesManager = $this->container->get('plugin.manager.irpf_specific_values');
  }

  /**
   * Test values.
   *
   * @covers \Drupal\info_irpf_calculator\IrpfCalculator::getValues
   */
  public function testGetValues() {
    $user_data = new IrpfUserData([
      'age' => 50,
      'annual_income' => 12000.00,
      'is_pension' => FALSE,
      'declaration_type' => IrpfUserDataInterface::DECLARATION_TYPE_INDIVIDUAL,
      'single_parent' => FALSE,
      'descendant' => 2,
      'descendant_under_3' => 1,
    ]);

    $values = $this->irpfCalculator->getValues($user_data);
    $regions = count($this->irpfSpecificValuesManager->getDefinitions());
    $this->assertCount($regions, $values);
  }

}

When I run it: vendor/bin/phpunit --filter IrpfCalculatorTest

It give me back this error:

There was 1 error:

1) Drupal\Tests\info_irpf_calculator\Kernel\IrpfCalculatorTest::testGetValues
Error: Call to a member function get() on null

/var/www/html/web/modules/custom/info_irpf_calculator/src/Plugin/IrpfSpecificValues/AndalusiaIrpfSpecificValues.php:55
/var/www/html/web/modules/custom/info_irpf_calculator/src/Plugin/IrpfSpecificValues/IrpfSpecificValues.php:75
/var/www/html/web/modules/custom/info_irpf_calculator/src/IrpfCalculator.php:46
/var/www/html/web/modules/custom/info_irpf_calculator/tests/src/Kernel/IrpfCalculatorTest.php:63

The line in AndalusiaIrpfSpecificValues.php is:

  protected function getMinPersonal(IrpfUserDataInterface $user_data) {
    $elements = $this->taxValues->get('get_min_personal_fieldset');
    $value = $this->getMinPersonalTrait($elements, $user_data);
    return $value;
  }

$this->taxValues comes from the construct:

$this->taxValues = $this->entityTypeManager->getStorage('info_irpf_tax_values')->load(self::NAME);

The problem is that when I run the test the class doesn't load the configuration, but I use the website it works fine.

How can I make to load the configuration when I run the test?

Thanks.