Obtener Valor de RadioButton (Grupo)

HTML:

<form id="test">
<label><input type="radio" name="test" value="A"> A</label>
<label><input type="radio" name="test" value="B" checked> B</label>
<label><input type="radio" name="test" value="C"> C</label>
</form>

Javascript:

document.querySelector('input[name="test"]:checked').value;