I am trying to write a test class for the following trigger:

trigger WebToCaseCountry on Case (after insert)
{
    
    Set<String> countries = new Set<String>();
    for (Case c : Trigger.new)
    {
        if (!String.isEmpty(c.CountryWebFormText__c) && c.Newsletter__c == TRUE)
        {
            countries.add(c.CountryWebFormText__c);
        }
    }
    
    if (countries.size() > 0)
    {
        Set<String> filteredCountries = new Set<String>();
        for (Area__c a : [select Name from Area__c where Name in :countries])
        {
            filteredCountries.add(a.Name);
        }
        if (filteredCountries.size() > 0)
        {
            Case[] caseUpdates = new Case[] {};
            Contact[] contactUpdates = new Contact[] {};
            for (Case c : Trigger.new)
            {
                if (filteredCountries.contains(c.CountryWebFormText__c))
                {
                    caseUpdates.add(new Case(Id = c.Id, Country_of_Origin__c = c.CountryWebFormText__c));
                    if (c.ContactId != null)
                    {
                        contactUpdates.add(new Contact(Id = c.ContactId, Country__c = c.CountryWebFormText__c));
                    }
                }
            }
            update caseUpdates;
            update contactUpdates;
        }
    }
}

But I am getting an error with the insert statement when I try to execute it in Execute Anonymous. This is the error that I receive: "Line: 2, Column: 1 System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, WebToCaseCountry: execution of AfterInsert caused by: System.StringException: Invalid id: CA Trigger.WebToCaseCountry: line 28, column 1: []"

This is my Test Class at the moment:

@isTest
public class WebToCaseCountryTest
{
    
    public static testMethod void testTrigger()
    {
        Case c = new Case (Id = '500g000000CoMzp');
        Case caseObj = new Case(Id = c.Id, CountryWebFormText__c ='CA', Newsletter__c = TRUE);
        insert caseObj;
        System.debug(caseObj);
        
        System.assert(caseObj.Country_of_Origin__c == caseObj.CountryWebFormText__c);
        
        
    }
}