Developing Mobile Applications with Force.com and Sencha Touch - Part 1, Step 7: Replace Your Mock Data With The Real Thing - Apex Controller

PocketCRMLeadController1.cls

public class PocketCRMLeadController {
    private string leads;

    //Constructor.
    public PocketCRMLeadController() {

        //Fetch a limited set of Leads to return to the Sencha Data Store on load. 
        List < Lead > leadsList = [SELECT
                                              FirstName
                                              , LastName
                                              , Company
                                              , Title
                                              , Phone
                                              , Email
                                              , Status 
                                            FROM Lead LIMIT 25];

        //Serialize the list as JSON and assign to the private string member.
        leads = JSON.serialize(leadsList);
        system.debug('Leads as JSON: ' + leads);

    }

    //Public getter method to return the Leads as JSON to the view.
    public String getLeads() {

        return leads;

    }

    //UnitTest for code coverage.
    testMethod static void canTestConstruction() {

        //Build some mock data for the test.
        List < Lead > leadList = new List < Lead > ();
        for (Integer i = 0; i < 10; i++) {
            leadList.add(new Lead(
            Firstname = 'Test', Lastname = 'Lead' + String.valueOf(i), Company = 'Acme', Status = 'Open - Not Contacted'));
        }

        //Insert mock leads
        INSERT leadList;

        //Instantiate the controller which will fetch the Leads.
        PocketCRMLeadController c = new PocketCRMLeadController();
        system.assertNotEquals(c.getLeads(), null);

        //Output to the debug for visual confirmation during testing.    
        system.debug(leadList);
        system.debug(c.getLeads());
    }

}

Error fixed - needed Status field in SOQL query, required for grouping in listview.