Overview

Below is a sample test class for Accounting Seed's Payable object. This class can be used to test whether your code is working as expected. 

@IsTest
 private class PayableExampleTest {
     @IsTest
     static void createPayable() {
 
         // —— DATA PREPARATION ——
 
         // insert 1 Account
         Account acct = new Account(
                 Name = 'Test Account');
         insert acct;
 
         // insert 1 Accounting Period
         AcctSeed__Accounting_Period__c acctPeriod = new AcctSeed__Accounting_Period__c(
                 Name = '1991-10',
                 AcctSeed__Start_Date__c = Date.newinstance(1991, 10, 1),
                 AcctSeed__End_Date__c = Date.newinstance(1991, 10, 31),
                 AcctSeed__Status__c = 'Open');
         insert acctPeriod;
         // 1 Cash GL-Account
 
         AcctSeed__GL_Account__c cashGL = new AcctSeed__GL_Account__c(
                 Name = '1000-Cash',
                 AcctSeed__Active__c = true,
                 AcctSeed__Type__c = 'Balance Sheet',
                 AcctSeed__Bank__c = true,
                 AcctSeed__Sub_Type_1__c = 'Assets',
                 AcctSeed__Sub_Type_2__c = 'Cash');
         insert CashGL;
 
         // insert 4 billing formats
         AcctSeed__Billing_Format__c[] PDFformats = new List<AcctSeed__Billing_Format__c>();
         PDFformats.add(
                 new AcctSeed__Billing_Format__c(
                         Name = 'Default Billing Product',
                         AcctSeed__Visualforce_PDF_Page__c = 'BillingProductPDF',
                         AcctSeed__Default_Email_Template__c = [Select Id, DeveloperName From EmailTemplate limit 1].DeveloperName,
                         AcctSeed__Type__c = 'Billing',
                         AcctSeed__Sort_Field__c = 'Name'
                 )
         );
 
         PDFformats.add(
                 new AcctSeed__Billing_Format__c(
                         Name = 'Default Billing Service',
                         AcctSeed__Visualforce_PDF_Page__c = 'BillingServicePDF',
                         AcctSeed__Default_Email_Template__c = [Select Id, DeveloperName From EmailTemplate limit 1].DeveloperName,
                         AcctSeed__Type__c = 'Billing',
                         AcctSeed__Sort_Field__c = 'Name'
                 )
         );
 
         PDFformats.add(
                 new AcctSeed__Billing_Format__c (
                         Name = 'Billing Outstanding Statement',
                         AcctSeed__Visualforce_PDF_Page__c = 'BillingOutstandingStatementPDF',
                         AcctSeed__Default_Email_Template__c = [Select Id, DeveloperName From EmailTemplate limit 1].DeveloperName,
                         AcctSeed__ReplyTo_Email__c = 'test3463464364646@gmail.com',
                         AcctSeed__Type__c = 'Outstanding Statement'
                 )
         );
 
         PDFformats.add(
                 new AcctSeed__Billing_Format__c (
                         Name = 'Billing Activity Statement',
                         AcctSeed__Visualforce_PDF_Page__c = 'BillingActivityStatementPDF',
                         AcctSeed__Default_Email_Template__c = [Select Id, DeveloperName From EmailTemplate limit 1].DeveloperName,
                         AcctSeed__ReplyTo_Email__c = 'test3463464364646@gmail.com',
                         AcctSeed__Type__c = 'Activity Statement'
                 )
         );
 
         PDFformats.add(
                 new AcctSeed__Billing_Format__c(
                         Name = 'Default Purchase Order',
                         AcctSeed__Visualforce_PDF_Page__c = 'BillingServicePDF',
                         AcctSeed__Default_Email_Template__c = [Select Id, DeveloperName From EmailTemplate limit 1].DeveloperName,
                         AcctSeed__Type__c = 'Purchase Order',
                         AcctSeed__Sort_Field__c = 'Name'
                 )
         );
 
         PDFformats.add(
                 new AcctSeed__Billing_Format__c(
                         Name = 'Default Packing Slip',
                         AcctSeed__Visualforce_PDF_Page__c = 'BillingServicePDF',
                         AcctSeed__Default_Email_Template__c = [Select Id, DeveloperName From EmailTemplate limit 1].DeveloperName,
                         AcctSeed__Type__c = 'Packing Slip',
                         AcctSeed__Sort_Field__c = 'Name'
                 )
         );
 
         insert PDFformats;
         // insert 1 Ledger records
         AcctSeed__Ledger__c ledger = new AcctSeed__Ledger__c(
                 Name = 'Actual',
                 AcctSeed__Type__c = 'Transactional',
                 AcctSeed__Default_Bank_Account__c = CashGL.id,
                 AcctSeed__Default_Billing_Format__c = PDFformats[0].Id,
                 AcctSeed__Billing_Outstanding_Statement_Format__c = PDFformats[2].Id,
                 AcctSeed__Billing_Activity_Statement_Format__c = PDFformats[3].Id,
                 AcctSeed__Default_Purchase_Order_Format__c = PDFformats[4].Id,
                 AcctSeed__Default_Packing_Slip_Format__c = PDFformats[5].Id);
         insert ledger;
 
         // --- START HERE ---
         // Create Payable RECORD
         AcctSeed__Account_Payable__c invoice = new AcctSeed__Account_Payable__c(
                 AcctSeed__Payee_Reference__c = '1',
                 AcctSeed__Vendor__c = acct.Id,
                 AcctSeed__Accounting_Period__c = acctPeriod.Id,
                 AcctSeed__Ledger__c = ledger.Id
 
         );
 
         insert invoice;
         System.assertEquals(1, [Select count() FROM AcctSeed__Account_Payable__c WHERE Id = :invoice.Id]);
     }
 }