Lead trigger test fails - newbie alert!

Question

Trying to write a trigger to set a lookup field (Account) on the Lead object, which is based on Account ID as a string that is passed through from an external form)... I have a working trigger (100% coverage), and what seems to be a working test class, but when I deploy in production, the validation fails due to 0% code coverage. No other exceptions. I know this should be simple! I also know it's a bad idea to pass a static ID in the test, but don't know how else to test this? If successful, will be using a custom Lead conversion tool to create new custom objects that are automatically associated with the Account ID with limited user input. Thanks in advance!!

Trigger Code:

trigger LeadSetAccount on Lead (before insert) {
// Initiate a For Loop
    for (Lead newLead : Trigger.new) {
// If a Lead has a value in the Account ID field, then execute
        if (newLead.Account_ID__c!=null) {
// Set Account ID based on the Account_ID string
    String AccountString = newLead.Account_ID__c;
    Id AccountID = AccountString;
    newLead.Account__c = AccountID;
        }
    }
}

Test Class:

@IsTest
public class TestLeadSetAccount {

//Sets method as testMethod, so any new data generated by this test will be removed after execution
    static testmethod void insertLead() {
//Name new Lead
         Lead newLead = new Lead();
// Set values for new Lead
         newLead.Company = 'Treadway';
         newLead.FirstName = 'Marty';
         newLead.LastName = 'Treadway';
         newLead.Status = 'Open';
         newLead.Account_ID__c = '001c000000gULKV';
// Insert new Lead
         insert newLead;
    }   
}

Answer 1

I don't understand why coverage is a problem here; I would have through that using an Account ID that doesn't exist would cause a test failure with some code coverage not 0% coverage. Double check that both the trigger and the test are being deployed.

It is common to insert the necessary objects in a test. In this case the test might be coded like this:

@isTest
public class TestLeadSetAccount {
    @isTest
    static void insertLead() {
         Account a = new Account(Name = 'Acme');
         insert a;
         Lead l = new Lead(
                 Company = 'Treadway',
                 FirstName = 'Marty',
                 LastName = 'Treadway',
                 Status = 'Open',
                 Account_ID__c = String.valueOf(a.Id)
                 );
         insert l;
         System.assertEquals(
                 a.Id,
                 [select Account__c from Lead where Id = :l.Id].Account__c
                 );
    }   
}

But wouldn't it be simpler to set the Account ID directly in the Lead.Account__c in the first place and avoid the need for the trigger?