Cannot get JSON response from custom controller

I have seen several examples where JSON is returned from a custom controller. I have tried many different ways and every time my controller always returns HTML. I do not know why it does not work.

My Controller:

namespace Test\Module\Controller\Index;

use Magento\Framework\App\Action\Context; use Magento\Framework\Controller\ResultFactory;

class Test extends \Magento\Framework\App\Action\Action {

 /* @var \Magento\Framework\Controller\Result\JsonFactory   */    

  private $resultJsonFactory;

  public function __construct(
    \Magento\Backend\App\Action\Context $context,
    \Magento\Framework\Controller\Result\JsonFactory $resultJsonFactory   ) {
    parent::__construct($context);
    $this->resultJsonFactory = $resultJsonFactory;   }

    public function execute() {
    $response['status'] = "SUCCESS";

    $resultJson = $this->resultJsonFactory->create();
    $resultJson->setData($response); // array value set in Json Result Data set

    return $resultJson; // return json object
    } }

I am calling the controller with Ajax. My Ajax request:

  function ajaxRequest() {
    try {
      jQuery.ajax({
        url: 'my-controller-url',
        dataType: "json",
        type: "POST",
        data: data.cart })
      .done(function( json ) {
        if (json.status === "SUCCESS") {
          toggleConfirmOverlay();
          progress[data.currentSection].className = 'done';
          displayPopupCart();
        } else {
          alert( "Sorry, there was a problem!" );
          console.log(json.error);
        }
      })
      .fail(function( xhr, status, errorThrown) {
        alert( "Sorry, there was a problem!" );
        console.log( "Error: " + errorThrown );
        console.log( "Status: " + status );
        console.dir( xhr );
      })
      .always(function( xhr, status ) { //        toggleSpinner();
      });
    } catch (e) {
      console.log('error: ' + e);
    }   }

In the JS console I receive an error that JSON cannot be decoded. Inspecting the result shows a full HTML page with navigation.