I'm new to salesforce and would like to create a sample vf page which accept user input and once I clicked on save it will get inserted into my custom object and I want another button to show the record of the custom object on vf page, can you please help me for the code of vf and controller.
Its just for my learning purpose.

I have this very simple class..  

trigger RestrictContactByName on Contact (before insert, before update) {
    //check contacts prior to insert or update for invalid data
    For (Contact c : Trigger.New) {
        if(c.LastName == 'INVALIDNAME') {   //invalidname is invalid
            c.AddError('The Last Name "'+c.LastName+'" is not allowed for DML');
        }
    }
}

.. and the corresponding Test Class:  

@isTest
private class TestRestrictContactByName {

	@isTest static void metodoTest() {
		
		List listaContatti = new List();
		Contact c1 = new Contact(FirstName='Francesco', LastName='Riggio');
		Contact c2 = new Contact(LastName = 'INVALIDNAME');
		listaContatti.add(c1);
		listaContatti.add(c2);
		
		//insert listaContatti;
		
		// Perform test
        Test.startTest();
        Database.SaveResult [] result = Database.insert(listaContatti, false);
        Test.stopTest(); 
		
		c1.LastName = 'INVALIDNAME';
		update c1;
       		
	}
	
}

When I run the Test class from the Developer Console I get 100% of coverage on the RestrictContactByName class but, when I check the challenge on the trailhead it returns the error:

Challenge not yet complete... here's what's wrong: The 'RestrictContactByName' class did not achieve 100% code coverage via your test methods

Has someone had my same issue?