NodeList objects are collections of nodes. In some cases, the NodeList is live, which means that changes in the DOM automatically update the collection.
In other cases, the NodeList is static, where any changes in the DOM does not affect the content of the collection. The document.querySelectorAll() method returns a static NodeList, for instance.

It's possible to loop over the items in a NodeList using a for loop:

for (let i = 0; i < myNodeList.length; i++) {

  let item = myNodeList[i];

}

for...of loops will loop over NodeList objects correctly:

const list = document.querySelectorAll('input[type=checkbox]');

for (let checkbox of list) {

  checkbox.checked = true;

}

You can use item() method to get an item by its index. For instance, this is how you can get id of the first <div> on some page:

document.querySelectorAll("div").item(0).id

In your case, you have an array and it contains an element of type NodeList.
So, when you do test._groups[0] you get the first element of your array and this element is NodeList and you need to work with it as with NodeList (see above)! For instance:

const arr = [1,2]; // simple array

// arr[0] is 1.

// in your case you have an array, but elements in that array are of type NodeList 

// (that's why console shows something like [NodeList(...)])



// when you get something from your array - it will be NodeList

// hence you can iterate over it or get some particular item like

test._groups[0].item(0).ariaAtomic

There are a lot more useful methods. Check docs for more details.