How to use Safari Technology Preview in nightwatch?

I didn't find any information on how to properly setup the nightwatch config using Safari technology preview.

I've tried something like this:

module.exports = {
    "src_folders": [
        "suites"
    ],
    "output_folder": "reports",
    "custom_commands_path": "commands",
    "page_objects_path": "pageObjects",
    "globals_path": "globals.js",
    "selenium": {
        "start_process": true,
        "server_path": seleniumServer.path,
        "host": "127.0.0.1",
        "port": 4444,
        "log_path": "logs",
        "cli_args": {
            "webdriver.chrome.driver": chromedriver.path,
            "webdriver.firefox.driver": '/usr/bin/geckodriver',
            "webdriver.safari.driver": '/usr/bin/safaridriver'
        }
    },
    "test_settings": {
        "default": {
            "launch_url": "http://google.com",
            "screenshots": {
                "enabled": true,
                "on_failure" : true,
                "on_error" : true
            },
            "globals": {
                "waitForConditionTimeout": 5000,
                "retryAssertionTimeout": 5000
            },
            "desiredCapabilities": {
                "browserName": "safari",
                "browserVersion": "12",
                "technologyPreview": true
            },
            "skip_testcases_on_fail": false,
            "end_session_on_fail": false
        }
    }
};

But after execution I get this error:

{ value: 
   { message: 'Could not create a session: A browser with name \'safari\' version \'12\' could not be found on the system.\nBuild info: version: \'3.13.0\', revision: \'2f0d292\', time: \'2018-06-25T15:32:19.891Z\'\nSystem info: host: \'Boostas-MacBook-Pro-5.local\', ip: \'fe80:0:0:0:100a:70f9:d6d7:cbfc%en0\', os.name: \'Mac OS X\', os.arch: \'x86_64\', os.version: \'10.13.6\', java.version: \'10.0.1\'\nDriver info: driver.version: unknown\nremote stacktrace: ',
     error: 'session not created' },
  status: 33 }

Note: If I set technologyPreview to false the test will be run in Safari browser.

Hope you guys can help me!

Those two options worked in my case in nightwatch.json to launch Safari Technology Preview :

  "desiredCapabilities": {
    "browserName": "safari",
    "safari.options": {"technologyPreview": true},
  }

Useful reference : https://macops.ca/using-safari-technology-preview-with-selenium-webdriver/

Hope this helps !