<form method="post" action="" accept-charset="UTF-8" id="testForm">
  {{ csrfInput() }}
  <input type="hidden" name="action" value="test/test">
  <button type="submit">Test</button>
</form>

<script type="text/javascript">
   window.csrfTokenName = "{{ craft.config.csrfTokenName|e('js') }}";
   window.csrfTokenValue = "{{ craft.request.csrfToken|e('js') }}";
</script>
<script>
$("#testForm").submit(function (e) {
    e.preventDefault();
    var data = [];
    data["test"] = "test";
    data[csrfTokenName] = csrfTokenValue;
    $.post('/', data, function(response) {
        console.log(response);
    });
});
</script>