public class CreatePayableInvoiceController {
    
     private final Multi_Vendor_Invoice__c MVI;
        public ID newRecordId {get;set;}
    public CreatePayableInvoiceController(ApexPages.StandardController controller){
                        this.MVI = (Multi_Vendor_Invoice__c)controller.getRecord();

    }
    
    public pagereference createPayableInvoice(){
        
        if(MVI.Status__c != 'Approved'){
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, 'This Invoice must be Approved before a Payable Invoice can be generated.'));
            return Null;        
        }
        
        
        Date Today = Date.Today();
            //get invoice setting
            Vendor_Invoice_Settings__c settings = Vendor_Invoice_Settings__c.getValues('Default Vendor Settings');
        
        
            Map<String, String> GLAsMap = new Map<String, String>();
       
        
        //and a list 
        List<String> GLAsMaplist = new List<String>();
        GLAsMaplist.add(settings.Billable_Expenses_GLA__c);
        GLAsMaplist.add(settings.Non_Billable_Expenses_GLA__c);
        GLAsMaplist.add(settings.Adjustment_GLA__c);
        //GLAsMaplist.add(settings.TimeDefaultGLAAccount__c);
        
        //get GLA's
       List<c2g__codaGeneralLedgerAccount__c> GLAs = [SELECT id, Name 
                                                               from c2g__codaGeneralLedgerAccount__c
                                                               where Name in: GLAsMaplist];
       
        for(c2g__codaGeneralLedgerAccount__c GLA : GLAs){
            GLAsMap.put(GLA.Name, GLA.id);
        }
        
        
         
        
        //create Payable Invoice
        c2g__codaPurchaseInvoice__c PI = new c2g__codaPurchaseInvoice__c();
        PI.c2g__Account__c = MVI.Account__c;
        //PI.ThisWilWork__c = MVI.id;
        PI.c2g__Reference1__c = MVI.Name;
        //PI.ffap__DeriveDueDate__c = true;
        //PI.ffap__DerivePeriod__c = true;
        PI.c2g__InvoiceDate__c = MVI.Invoice_Date__c;
        PI.c2g__AccountInvoiceNumber__c = MVI.Vendor_Invoice_Number__c;
        PI.c2g__Period__c = MVI.Period__c;
       PI.c2g__InvoiceCurrency__c = MVI.Accounting_Currency_lookup__c;
        //PI.ffap__DeriveCurrency__c = true;
       PI.c2g__InvoiceDescription__c = MVI.Invoice_Description__c;
        system.debug('Invoice trying to create: ' + PI);
        try{
            insert PI;
            system.debug('Created Invoice: ' + PI);
        }catch(DMLException e){
            system.debug('FAILED TO CREATE INVOICE: ' + PI + 'GOT ERROR: ' + e);
            ApexPages.addMessages(e);
        
            
            Return Null;
        }
        
        
        //get a list of all the invoice items
            List<Multi_Vendor_Invoice_Item__c> MVIIs = [Select id, Timecard__c, Vendor_Invoice__c, Line_Type__c, Quantity__c, Rate__c, Value__c, Expense__c, CurrencyIsoCode, Project_Name__c, Region_Name__c, Line_Description__c, Billable__c, Resource__r.Name, First_Date__c, Last_Date__c 
                                                       from Multi_Vendor_Invoice_Item__c
                                                       WHERE Vendor_Invoice__c =: MVI.id];
        
        //create Payable Invoice Items List (regular) and add to the list depending on the MVII line type
        List<c2g__codaPurchaseInvoiceLineItem__c> PILIs = New List<c2g__codaPurchaseInvoiceLineItem__c>();
        
        //create Payable Invoice Expense Line Items list and add to the list depending on the MVII line type
        List<c2g__codaPurchaseInvoiceExpenseLineItem__c> PIELs = New List<c2g__codaPurchaseInvoiceExpenseLineItem__c>();
        
        //Create list of Regions Reflected by Invoice Items
        Set<String> RegionNames = New Set<String>();
        
        For(Multi_Vendor_Invoice_Item__c MVI : MVIIs){
            RegionNames.add(MVI.Region_Name__c);
        }
       
        //get a list of dimensions from the region name list
        List<c2g__codaDimension1__c> Dimensions = [SELECT Id, Name, c2g__ExternalId__c 
                                                from c2g__codaDimension1__c 
                                                where Name in: RegionNames];
        
        //Create map for dimensions and Regions
        Map<String, c2g__codaDimension1__c> DimensionsAndRegions = new Map<String, c2g__codaDimension1__c>();
        for(c2g__codaDimension1__c Dimension : Dimensions){
            if(RegionNames.contains(Dimension.Name)){
                DimensionsAndRegions.put(Dimension.Name, Dimension);
            }
        }
        
        //create resource Set - Resource name as unique value
        //
        Set<String> ResourceSet = new Set<String>();
        //Create project set - Projcet name as unique value
        Set<String> ProjectSet = new Set<String>();
        
        
        //add relevant items to the lists
        for(Multi_Vendor_Invoice_Item__c MVII : MVIIs ){
            
            //Add to Resource Set
            ResourceSet.add(MVII.Resource__r.Name);
            ProjectSet.add(MVII.Project_Name__c);            
            
                //Create Purchase invoice item and assign properties 
                              c2g__codaPurchaseInvoiceExpenseLineItem__c PIEL = New c2g__codaPurchaseInvoiceExpenseLineItem__c();
 
             if(MVII.Line_Type__c == 'Timecard'){
                //Add to resource Map
                 
                 
                PIEL.c2g__NetValue__c = MVII.Value__c;
                PIEL.Timecard_Split__c = MVII.Timecard__c;
                PIEL.CurrencyIsoCode = MVII.CurrencyIsoCode; 
                PIEL.c2g__PurchaseInvoice__c = PI.id;
                 PIEL.ffpsai__Analysis1__c = MVII.Project_Name__c;
                 
                 if(DimensionsAndRegions.get(MVII.Region_Name__c) != NULL){
                      PIEL.c2g__Dimension1__c = DimensionsAndRegions.get(MVII.Region_Name__c).id;
 
                 }
                 
                 PIEL.c2g__LineDescription__c = MVII.Line_Description__c;
                // PIEL.c2g__GeneralLedgerAccount__c = GLAsMap.get(settings.TimeDefaultGLAAccount__c);
                
                system.debug(PIEL.id);
                system.debug(PIEL.c2g__PurchaseInvoice__c);
                PIELs.add(PIEL);
            }
            if(MVII.Line_Type__c == 'Expense'){
                
                
                PIEL.c2g__NetValue__c = MVII.Value__c;
                PIEL.ffpsai__Expense__c = MVII.Expense__c;
                PIEL.c2g__PurchaseInvoice__c = PI.id;
                PIEL.ffap__SetGLAToDefault__c = FALSE;
                PIEL.ffpsai__Analysis1__c = MVII.Project_Name__c;
                if(DimensionsAndRegions.get(MVII.Region_Name__c) != NULL){
                    PIEL.c2g__Dimension1__c = DimensionsAndRegions.get(MVII.Region_Name__c).id;
                    
                 }
                PIEL.c2g__LineDescription__c = MVII.Line_Description__c; 
                if(MVII.Billable__c == TRUE){
                    PIEL.c2g__GeneralLedgerAccount__c = GLAsMap.get(settings.Billable_Expenses_GLA__c);
                }else{
                    PIEL.c2g__GeneralLedgerAccount__c = GLAsMap.get(settings.Non_Billable_Expenses_GLA__c);
                }
                system.debug('PIEL: ' + PIEL);
                
                PIELs.add(PIEL);
            }
            if(MVII.Line_Type__c == 'Invoice Adjustment'){
                if(MVII.Value__c == NULL){
                    PIEL.c2g__NetValue__c = 0.00;
                }else{
                    PIEL.c2g__NetValue__c = MVII.Value__c; 
                }
                 PIEL.c2g__PurchaseInvoice__c = PI.id;
                 PIEL.ffap__SetGLAToDefault__c = FALSE;
                 PIEL.c2g__GeneralLedgerAccount__c = GLAsMap.get(settings.Adjustment_GLA__c);
                 PIEL.c2g__LineDescription__c = MVII.Line_Description__c;
                 PIEL.ffpsai__Analysis1__c = MVII.Project_Name__c;
                   
                 if(DimensionsAndRegions.get(MVII.Region_Name__c) != NULL){
                    PIEL.c2g__Dimension1__c = DimensionsAndRegions.get(MVII.Region_Name__c).id;
                    
                 }
                 PIELs.add(PIEL);


            }
            
        }
        
        try{
                insert PILIs;
            }catch(DMLException e){
                system.debug(e);
                ApexPages.addMessages(e);
                return NULL;

            }
        
        try{
            insert PIELs;
        }catch(DMLException e){
            system.debug(e);
            ApexPages.addMessages(e);
            return NULL;
        }
        
        MVI.Payable_Invoice__c = PI.id;
        
        try{
            update MVI;
        }catch(DMLException e){
            system.debug(e);
        }
        
        //add all keys from resource map to set and then iterate over them to grab values from map
        String descriptionString = '';
        for(String project : ProjectSet){
            descriptionString = descriptionString + ', ' + project; 
        }
        //remove the first ","
        descriptionString = descriptionString.removeStart(',');
        descriptionString = descriptionString + ': ';
            
        String ResourceList = '';
        for(String resource: ResourceSet){
            ResourceList = ResourceList + ', ' + resource;
        }
        
        ResourceList = ResourceList.removeStart(',');//remove the leading comma
        //add the two strings together to make the full description
        descriptionString = descriptionString + ResourceList;
        
        system.debug('invoice description' + descriptionString);
                //set description
        PI.c2g__InvoiceDescription__c = descriptionString;
        
        system.debug('PI.c2g__InvoiceDescription__c' + PI.c2g__InvoiceDescription__c);
        try{
            update PI; 
        }catch(DMLException e){
            system.debug(e);
        }
        return new PageReference('/'+PI.id);
    }
}

Trying to upload this piece of code and 



Bunch of test methods failing on me.

The code is exactly what the production has right now.

So technically there is no change associated but it fails.

I am doing this because initally

//create Payable Invoice
        c2g__codaPurchaseInvoice__c PI = new c2g__codaPurchaseInvoice__c();
        PI.c2g__Account__c = MVI.Account__c;
        //PI.ThisWilWork__c = MVI.id;

I was trying to make PI.ThisWilWork thing work but now I have it commented out to see if the original was even properly working.

I know of test start method and test stop method but I am not quite sure where I would put them.

Note that I have not written the test codes and the class and I am only trying to add a line to a class in order to make something work.

It will be appreciated if you could tell me what I am doing wrong.

Thank You

I wrote a class 

public with sharing class SlackOpportunityPush {
    
    
    // To publish Opportunity values in form of a String//
    public static final String slackURL = 'https://hooks.slack.com/services/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';
    
    public class Oppty {
        @InvocableVariable(label='Opportunity Name')
        public String opptyName;
        
        @InvocableVariable(label='Owner')
        public String Owner;
        
        @InvocableVariable(label='Opportunity Amount')
        public String Amount;
        
        @InvocableVariable(label='Account Development Owner')
        public String AccountDE;
        
        @InvocableVariable(label='Account')
        public String Account;
    }
     
    @InvocableMethod(label='Push to Slack')
    
    public static void postToSlack(List<Oppty> oppties) { 
        Oppty o = oppties[0]; // If bulk, only post first to avoid overloading Slack channel
        Map<String,Object> msg = new Map<String,Object>();
        msg.put('text',  '\n Opportunity Won !  Congrats to Opportunity Owner !  :-  ' +o.Owner +   '\n and Account Development Owner:-  '+ o.AccountDE + '\n who just closed Opportunity:-  ' +o.opptyName +   '\n associated to Account:- ' + o.Account +'\n for Opportunity Amount:- $ ' + o.Amount);
        
        System.debug('Called msg.put');
        System.debug('OpportunityOwner '+o.Owner);
        System.debug('OpportunityAccount '+o.Account);
        System.debug('OpportunityAmount '+o.Amount);
        
        
        msg.put('mrkdwn',true);
        String body = JSON.serialize(msg);    
        System.enqueueJob(new QueueableSlackCall(slackURL,'POST',body));
    
    
    
    }
     
    public class QueueableSlackCall implements System.Queueable, Database.AllowsCallouts {
         
        public final String url;
        public final String method;
        public final String body;
         
        public QueueableSlackCall(String url,String method,String body) {
            this.url = url;
            this.method = method;
            this.body = body;
        }
         
        public void execute(System.QueueableContext ctx) {
            HttpRequest req = new HttpRequest();
            req.setEndpoint(url);
            req.setMethod(method);
            req.setBody(body);
            Http http = new Http();
            HttpResponse res = http.send(req);
        }
 
    }
    
}

Test class 

@isTest
private class SlackOpportunityTest {
    

static testMethod void testpostToSlack() {
SlackOpportunityPush.Oppty opt = new SlackOpportunityPush.Oppty();
opt.opptyName = 'Unit Test Opt';
opt.Owner = 'Unit Test Owner';


List<SlackOpportunityPush.oppty> lis = new List<SlackOpportunityPush.oppty>();
lis.add(opt);
SlackOpportunityPush.postToSlack(lis);

System.assertEquals(lis, lis); 
    
}
     
}

Code coverage is now 100% but while deploying the classes I get error:

​Methods defined as TestMethod do not support Web service callouts 
Stack Trace: null