Before Trigger and its unit test

ContactBeforeTrigger.trg

Trigger ContactBeforeTrigger on Contact (before insert) {
    for(Contact c : Trigger.new){
        c.Title = 'Admin';
    }
}

ContactBeforeTriggerTest.cls

@isTest
public class ContactBeforeTriggerTest {
    public static testMethod void testOne(){
        //Must create a test Account for the test Contact!
        Account a = new Account(Name = 'Test Account');
        insert a;
        
        //Now create your test Contact
        Contact c = new Contact(LastName = 'name', AccountId = a.Id);
        insert c;
        
        //Query to retrieve the Title field value for your Contact
        c = [Select Title from Contact where Id = :c.Id];
        
        //Assert that what you expect is what is actually the field value
        System.assertEquals('Admin', c.Title);
    }
    public static testMethod void testMany(){
        //Must create a test Account for the test Contacts!
        Account a = new Account(Name = 'Test Account');
        insert a;
        
        //Use a for-loop to populate a List of test Contacts
        List<Contact> testContacts = new List<Contact>();
        for(Integer i = 0; i < 2 ; i++){
            Contact c = new Contact(LastName = 'name' + i,//Use i to make each name unique
                                   AccountId = a.Id);
            testContacts.add(c);
        }
        insert testContacts;
        
        //Bulk Tests also require bulk assert tests
        for(Contact c : [Select Title from Contact]){
            System.assertEquals('Admin', c.Title);
        }
    }
}