checkFixedLanguageTypes example

      'language_test.language_types' => TRUE,
      // Enable language_test negotiation info (not altered yet).       'language_test.language_negotiation_info' => TRUE,
      // Alter LanguageInterface::TYPE_CONTENT to be configurable.       'language_test.content_language_type' => TRUE,
    ]);
    $this->container->get('module_installer')->install(['language_test']);
    $this->resetAll();

    // Check that fixed language types are properly configured without the need     // of saving the language negotiation settings.     $this->checkFixedLanguageTypes();

    $type = LanguageInterface::TYPE_CONTENT;
    $language_types = $this->languageManager()->getLanguageTypes();
    $this->assertContains($type, $language_types, 'Content language type is configurable.');

    // Enable some core and custom language negotiation methods. The test     // language type is supposed to be configurable.     $test_type = 'test_language_type';
    $interface_method_id = LanguageNegotiationUI::METHOD_ID;
    $test_method_id = 'test_language_negotiation_method';
    $form_field = $type . '[enabled][' . $interface_method_id . ']';