I have created a class that links a case with the case comment for a visualforce page but for the life of me I cannot remember how I write a test class for the apex class.

The class I require tests for is:

public class Caselinktocomment
{
    public CaseComment comment { get; set; }
    public String commentText {get; set;}
    public String PublicPrivateAction {get; set;}


    public Caselinktocomment(ApexPages.StandardController stdController) 
    {
        this.comment = new CaseComment(ParentId = stdController.getId());
    }

    public PageReference saveComment()
    {
        insert comment;
        return null;
    }
}

The test Class I have written is:

@istest

Private class Caselinktocommenttests {
    

    static testmethod void createtestdata() {
    Id RecordId = Schema.SObjectType.Case.getRecordTypeInfosByDeveloperName().get('Service_Desk').getRecordTypeId();
        Case tcase = new Case();
        tCase.Status = 'New';
        tCase.Description = 'This ticket has been created as a test';
        tCase.Subject = 'Test Case';
        tCase.RecordTypeId = RecordId;
        tCase.Reason = 'Access Requests';
        tCase.Origin = '';Phone
        
        INSERT tCase;
        
        CaseComment tComment = new CaseComment();
        tComment.ParentId = tCase.Id;
        tComment.CommentBody = 'Test Comment';
        tComment.IsPublished = FALSE;
        tComment.IsNotificationSelected= FALSE;
        Test.startTest();
        INSERT tComment;
        Test.stopTest();
        system.assertEquals(1, [SELECT count() From CaseComment], 'Test Comment');
        }   
}

The code coverage does not seem to increase. Can anyone advise where I have gone wrong.