StateFul_BatchClass

*************************Problem Statement*****************************************************
When StageName is changing, you have to:
1. break the field Value e.g. giving in format AUD 20,930.00 (USD 32,11.90)
2. And put 32,11.90 this in different field

Approach:
1. Writing trigger
2. Calling batch Apex from Trigger to perform this operation
*************************************************************************************************

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Trigger<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
trigger ExtractCurr on Opportunity (before Update) {
    
    try{
        if(trigger.isExecuting && trigger.isBefore && trigger.isUpdate){
            for(Opportunity op:trigger.new){
                if(op.StageName!=trigger.oldmap.get(op.Id).StageName){
                    
                    //Calling batch class from Trigger
                    BatchOpportunityCurrency btOpCu= new BatchOpportunityCurrency();
                    Database.executebatch(btOpCu,10);  //controlling batch size
                }
            }
        }
    }catch(exception ex){
        system.debug('@@@@ ex.getLineNumber: '+ex.getLineNumber());
        system.debug('@@@@ ex.getLineNumber: '+ex.getMessage());
    }
}

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Batch Class<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

public class BatchOpportunityCurrency implements Database.Batchable<Sobject>, Database.Stateful{
    
    integer RecordProcessed=0;
    integer RecordFailed=0;
    list<Opportunity> lstOpPr= new list<Opportunity>();
    
    //start method
    public Database.QueryLocator start(Database.BatchableContext bc){
        
        return database.getQueryLocator('select Id, Multi_currecy__c, USD__c from Opportunity');
        
    }
    
    //execute method
    public void execute(Database.BatchableContext bc, list<Opportunity>records){
        list<Opportunity> lstOpp= new list<Opportunity>();
        for(Opportunity op:records){
            string USDCurr = string.ValueOf(op.Multi_currecy__c);
            string USDrate= USDCurr.substringAfter('USD');
            string USDfRate =USDrate.SubStringBefore(')');
            string FinalUSD=USDfRate;
            op.USD__c=FinalUSD;
            if(op.USD__c!=Null && op.USD__c!=''){
                RecordProcessed=RecordProcessed+1;
                lstOpPr.add(op);
                lstOpp.add(op);
            }
            else{
                RecordFailed=RecordFailed+1; 
            }}
        update lstOpp;
       
    }
    
    //finish method
    public void finish (Database.BatchableContext bc){
        AsyncApexJob job=[SELECT Id, CreatedDate, CreatedById, JobType, ApexClassId, Status, JobItemsProcessed, 
                          TotalJobItems, NumberOfErrors, CompletedDate, MethodName, 
                          ExtendedStatus FROM AsyncApexJob where Id=:bc.getJobId()] ;
        system.debug('@@@@ JobId: '+bc.getJobId());
        system.debug('@@@@ job: '+job);
        system.debug('@@@@ Records processed: '+RecordProcessed);
        system.debug('@@@@ Records failed: '+RecordFailed);
        system.debug('@@@@ lstOpPr: '+lstOpPr);
        system.debug('@@@@ lstOpPr size: '+lstOpPr.size());
        
    }
    
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Test Class%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@isTest
public class TestBatchOpportunityCurrency {
    
    @TestSetUp public static void CreateData(){
        try{
            Opportunity opp = new Opportunity();
            opp.Name='testOp';
            opp.CloseDate=system.today();
            opp.StageName='Prospecting';
            opp.Multi_currecy__c='AUD 20,930.00 (USD 32,11.90)';
            insert opp;
        }catch(exception ex){}
    }
    
    @isTest public static void TestMethod1(){
        try{
            Opportunity op=[select Id, Name,CloseDate,StageName,Multi_currecy__c,USD__c from Opportunity Limit 1];
            test.startTest();
            op.StageName='Qualification';
            update op;
            BatchOpportunityCurrency bc = new BatchOpportunityCurrency();
            Database.executebatch(bc);
            //update op;
            system.assertEquals(op.StageName,'Qualification');
            test.stopTest();
        }catch(exception ex){
            
        }}
    
    @isTest public static void TestMethod2(){
        try{
            Opportunity op=[select Id, Name,CloseDate,StageName,Multi_currecy__c,USD__c from Opportunity Limit 1];
            test.startTest();
            op.StageName='Qualification';
            op.Multi_currecy__c='AUD 20,930.00 (EUD 32,11.90)';
            update op;
            BatchOpportunityCurrency bc = new BatchOpportunityCurrency();
            Database.executebatch(bc);
            //update op;
            system.assertEquals(op.StageName,'Qualification');
            test.stopTest();
        }catch(exception ex){
            
        }  
    }
}