Salesforce Apex Testing Code Coverage Issues for Simple Webhook - testing

Question

I am very new at Salesforce and am stuck on writing testing for some webhooks - one as a button and one triggered upon opportunity creation.
Goal: Pass Test for Webhook (I have tested it manually in the sandbox many times and both webhooks work).
Question: Is there a very simple test or two that will show that the webhook work so I can pass this?
Apex Trigger 1: (button push triggering)
trigger WebhookTrigger on CustomObject (after insert) {
String url = 'https://webhook.sample.com';
String content = Webhook.jsonContent(Trigger.new, Trigger.old);
Webhook.callout(url, content);
}
Apex Trigger 2: (opportunity created triggering)
trigger opportunityCreatedTrigger on Opportunity (after insert) {
String url = 'https://webhook.sample1.com';
String content = Webhook.jsonContent(Trigger.new, Trigger.old);
Webhook.callout(url, content);
}
Apex Class: Webhook:
public class Webhook implements HttpCalloutMock {
public static HttpRequest request;
public static HttpResponse response;
public HTTPResponse respond(HTTPRequest req) {
request = req;
response = new HttpResponse();
response.setStatusCode(200);
return response;
}
public static String jsonContent(List<Object> triggerNew, List<Object> triggerOld) {
String newObjects = '[]';
if (triggerNew != null) {
newObjects = JSON.serialize(triggerNew);
}
String oldObjects = '[]';
if (triggerOld != null) {
oldObjects = JSON.serialize(triggerOld);
}
String userId = JSON.serialize(UserInfo.getUserId());
String content = '{"new": ' + newObjects + ', "old": ' + oldObjects + ', "userId": ' + userId + '}';
return content;
}
#future(callout=true)
public static void callout(String url, String content) {
if (Test.isRunningTest()) {
Test.setMock(HttpCalloutMock.class, new Webhook());
}
Http h = new Http();
HttpRequest req = new HttpRequest();
req.setEndpoint(url);
req.setMethod('POST');
req.setHeader('Content-Type', 'application/json');
req.setBody(content);
h.send(req);
}
}