Since CORs is a Browser only issue, best to test via HTML.
Below is a basic HTML file to edit the URL and test CORs.
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta http-equiv="Content-Style-Type" content="text/css">
<title>CORS Tester</title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.0/jquery.min.js"></script>
</head>
<body>
<H2>To view test result</H2>
<h3>Right click this page > Inspect Element > Console </h3>
<p id="out"></p>
<script>
console.log("starting ajax request to the resource.");
$.ajax
({type: "get",
contentType: "application/json; charset=UTF-8",
url: "https://api.github.com",
headers: {},
xhrFields: {
withCredentials: false
},
success: function(data)
{
console.log("API is CORS enabled");
$('#out').text('API is CORS enabled. Response:' + JSON.stringify(data));
console.log('Response:')
console.log(data)
},
done: function( jqXHR, textStatus ) {
console.log( "Request failed: " + textStatus + jqXHR );
},
});
console.log("ajax request sent.");
</script>
</body>
</html>