Hello, I have apex class like this:

public class TwilioChatterConversationClass {
public static void ContactPostChatter(Id contactRecordId, string message){  
        if (flag == true){
        flag = false;
        Contact c = [ Select id, name, related_referral__r.ownerid, related_referral__r.name, related_Referral__r.Referral_Account__r.name From Contact Where Id =: contactRecordId];

        ConnectApi.FeedItemInput feedItemInput = new ConnectApi.FeedItemInput();
        ConnectApi.MentionSegmentInput mentionSegmentInput = new ConnectApi.MentionSegmentInput();
        ConnectApi.MessageBodyInput messageBodyInput = new ConnectApi.MessageBodyInput();
        ConnectApi.TextSegmentInput textSegmentInput = new ConnectApi.TextSegmentInput();

        messageBodyInput.messageSegments = new List<ConnectApi.MessageSegmentInput>();
        
        mentionSegmentInput.id = c.related_referral__r.ownerid;
    
//hyperlink        
String fullFileURL = URL.getSalesforceBaseUrl().toExternalForm()+'/'+ c.id;   
ConnectApi.LinkCapabilityInput linkInput = new ConnectApi.LinkCapabilityInput();
linkInput.url = fullFileURL;
linkInput.urlName = c.name;
ConnectApi.FeedElementCapabilitiesInput feedElementCapabilitiesInput = new ConnectApi.FeedElementCapabilitiesInput();
feedElementCapabilitiesInput.link = linkInput;
feedItemInput.capabilities = feedElementCapabilitiesInput; 
//

        messageBodyInput.messageSegments.add(mentionSegmentInput);

 //  textSegmentInput.text = 'Referral, "' + c.related_referral__r.name  +  '".         Next of Kin,' + c.name +', has responded to your text: ' + message + ' To view their record <a href=https://centers.lightning.force.com/'+c.Id+'>click here.</a>' ;
   textSegmentInput.text = 'Referral, "' + c.related_referral__r.name  +  '".         Next of Kin,' + c.name +', has responded to your text: ' + message;
    messageBodyInput.messageSegments.add(textSegmentInput);

        feedItemInput.body = messageBodyInput;
        feedItemInput.feedElementType = ConnectApi.FeedElementType.FeedItem;
        feedItemInput.subjectId = c.related_referral__r.ownerid;
        
    
ConnectApi.ChatterFeeds.postFeedElement(Network.getNetworkId(), feedItemInput);
    return;
}
}
}
}

I'm trying test code like this, but it's not covering the class (see screenshot below). Any idea why not?

@isTest
public class TwilioTriggerTest {
@isTest
    static void TwilioTest(){
        contact c = new contact();
        c.lastname = 'Test';
        c.MobilePhone = '123456789';
        c.Responded_to_first_message__c = true;
        insert c;

        TwilioChatterConversationClass.ContactPostChatter(c.id, 'hey');
}}