Why is my Batch Apex test skipping the entire execute method?

Question

I've been staring at this for far too long so would VERY MUCH appreciate help on what's going on here! This should be a relatively straightforward Batch Apex from the Asychronous Apex trail. 

When I run the test, it runs the start and finish methods and skips execute entirely. 

Test class:

@isTest
public class LeadProcessorTest {

    @isTest
    public static void testLeadProcessor() {
     
        List<Lead> listOfLeads = new List<Lead>();
        
        for(Integer i = 0; i < 200; i++) {
            Lead l = new Lead();
            l.LastName = 'Testing' + i;
            l.Company = 'Test Company ABC';
            l.Status = 'Open - Not Contacted';
            l.LeadSource = 'Web';
            listOfLeads.add(l);
        }
        
        System.debug('Number of leads created ' + listOfLeads.size());
        insert listOfLeads;
    }
    
    @isTest static void test() {
        Test.startTest();
        LeadProcessor lp = new LeadProcessor();
        Id batchId = Database.executeBatch(lp);
        Test.stopTest();
    }

}

Lead Processor class:

global class LeadProcessor implements Database.Batchable<sObject> {
    Integer recordsProcessed = 0;
    
    global Database.QueryLocator start(Database.BatchableContext bc) {
        return Database.getQueryLocator('SELECT Id, LeadSource FROM Lead');
    }
    
    public void execute(Database.BatchableContext bc, List<Lead> leads){
        List<Lead> myLeads = new List<Lead>();
        for(Lead currl : leads) {
            currl.LeadSource = 'Dreamforce';
            myLeads.add(currl);
            recordsProcessed += 1; 
        }
        
        update myLeads;
    }
    
    public void finish(Database.BatchableContext bc) {
        System.debug('Number of records processed: ' + recordsProcessed);
    }
}

Answer 1

testLeadProcessor() and test() are separate unit tests, which execute in separate, isolated test data contexts. The Leads inserted will not be visible to test() because they're inserted in a distinct context.

Then, execute() is not being executed because the query in start() returns no records.

The fix is easy: annotate testLeadProcessor() with the Apex annotation that corresponds to its actual role in this test suite, @testSetup, instead of @isTest. That will result in it executing before each unit test in this class, and the data it creates will be visible to the code executed in those tests.