[SalesForce] Test class showing error : Converted Account empty for a Converted Lead.: [ConvertedAccountId]

I need to write as test class to cover

public without sharing class CMassConvert {
    public boolean hasErrors;
    public String errorMsg {get; set;}
    //constructora
    public CMassConvert() {}

    public List<Database.LeadConvertResult> MassConvert(List<Lead> listOfLeads) {
        if(listOfLeads != null && listOfLeads.size() > 0) {
            try {
                Map<Id, Account> mapOfAccounts = new Map<Id, Account>();
                List<Id> listOfContactIds = new List<Id>();
                List<Lead> updatedLeadsCB = new List<Lead>();
                Id UsrId;

                //Get Converted Lead status
                String convertedLeadStatusValue = [SELECT Id, MasterLabel FROM LeadStatus WHERE IsConverted=true LIMIT 1].MasterLabel;

                if(convertedLeadStatusValue == null || convertedLeadStatusValue == '')
                    convertedLeadStatusValue ='Closed - Converted';

                Set<String> setOfFistName = new Set<String>();
                Set<String> setOfLastName = new Set<String>();
                Set<String> setOfAddress = new Set<String>();
                Set<String> setOfCity = new Set<String>();
                Set<String> setOfState = new Set<String>();
                Set<String> setOfZip = new Set<String>();

                for(Lead led : listOfLeads) {
                    setOfFistName.add(led.FirstName);
                    setOfLastName.add(led.LastName);  
                    setOfAddress.add(led.Street);
                    setOfCity.add(led.City);
                    setOfState.add(led.State);
                    setOfZip.add(led.PostalCode); 

                }

                // Check for any duplicate contacts
                List<Contact> listOfContact = [SELECT Id, FirstName, LastName, MailingStreet,  
                                               MailingCity, MailingState, MailingPostalCode, AccountID 
                                               FROM Contact 
                                               WHERE FirstName IN :setOfFistName AND LastName IN :setOfLastName
                                               AND MailingStreet IN :setOfAddress AND MailingCity IN :setOfCity
                                               AND MailingState IN :setOfState AND MailingPostalCode IN :setOfZip];

                Map<String, Contact> mapOfSearchContacts = new Map<String, Contact>();

                for(Contact c : listOfContact) {
                    String key = '';

                    if(c.FirstName != null)
                        key += c.FirstName.toLowerCase();
                    if(c.LastName != null)
                        key += c.LastName.toLowerCase();
                    if(c.MailingStreet != null)
                        key += c.MailingStreet.toLowerCase();
                    if(c.MailingCity != null)
                        key += c.MailingCity.toLowerCase();
                    if(c.MailingState != null)
                        key += c.MailingState.toLowerCase();
                    if(c.MailingPostalCode != null)
                        key += c.MailingPostalCode.toLowerCase();    
                    if(mapOfSearchContacts.ContainsKey(key) == false) {
                        mapOfSearchContacts.Put(key, c);
                    }
                }

                // Map<Id, Contact> mapOfContacts = new Map<Id, Contact>([SELECT Id, AccountID FROM Contact WHERE Id IN :listOfContactIds]);
                List<Database.LeadConvert> listOfLeadConvert = new List<Database.LeadConvert>();

                for(Lead led : listOfLeads) {
                    Database.LeadConvert lc = new database.LeadConvert();

                    if(ConvertedLeadStatusValue != null && ConvertedLeadStatusValue != '') {
                        lc.setConvertedStatus(convertedLeadStatusValue);
                    }

                    lc.setLeadId(led.id);

                    String leadKey = '';

                    if(led.FirstName != null)
                        leadKey += led.FirstName.toLowerCase();
                    if(led.LastName != null)
                        leadKey += led.LastName.toLowerCase();
                    if(led.Street != null)
                        leadKey += led.Street.toLowerCase();
                    if(led.City != null)
                        leadKey += led.City.toLowerCase();
                    if(led.State != null)
                        leadKey += led.State.toLowerCase();
                    if(led.PostalCode != null)
                        leadKey += led.PostalCode.toLowerCase();

                    Contact c = mapOfSearchContacts.get(leadKey);

                    if(c != null && c.AccountID != null) {
                        lc.SetContactID(c.Id);
                        lc.SetAccountID(c.AccountID);
                    }

                    // updatedLeadsCB.add(led);
                    // Get current user id to fill into converted by field in Leads based on custom setting else use default user in Lead
                    Map<String, CMLeadSetting__c> mapOfCMLeadSetting = CMLeadSetting__c.getAll(); 
                    if(mapOfCMLeadSetting.containsKey('CMLead Conversion')) {
                        if( mapOfCMLeadSetting.get('CMLead Conversion').Logged_in_User_For_Conversion__c ) {
                            UsrId = UserInfo.getUserId();
                        } else {
                            UsrId = led.OwnerId;
                        }                                                
                    }
                    lc.setOwnerId(UsrId);
                    lc.setOpportunityName(led.company + '-' + String.valueof(Date.today()));
                    listOfLeadConvert.add(lc);
                }

                System.debug('Converting Leads: ' + listOfLeadConvert); 
                List<Database.LeadConvertResult> lcr = Database.convertLead(listOfLeadConvert);

                for (Database.LeadConvertResult sLCR : lcr) {
                    System.debug('Opportunity Id for ' + sLCR.getLeadId() + ' = ' + sLCR.getOpportunityId());
                }
                return lcr;
            } catch(Exception e) {
                system.debug(e.getMessage());
                //throw e;
                this.hasErrors = true;
                this.errorMsg = e.getMessage();
                return null;
            }              
        } else {
            return null;
        }                
    }    
}

For this I wrote my test class as

Account a = new Account (); 
a.Name = 'Account name';
insert a;

Lead l = new Lead();
l.Company = 'LeadCompany';
l.IsUnreadByOwner__c = true;
l.Description = 'leadDescription';
l.Status = 'Open - Not Contacted';
l.FirstName = 'LeadFirstname';
l.LastName ='Leadlastname';
l.Street = 'Closed - Converted';
l.City = 'LeadCity';
l.State = 'LeadState';
l.PostalCode = '09877';
l.IsConverted = true;
l.Account__c = a.id;

insert l;

/*
    id usrprofileId=userinfo.getProfileId();
    Database.LeadConvert lc = new database.LeadConvert();
    lc.setLeadId(l.id);
    lc.setDoNotCreateOpportunity(true);
    lc.setOwnerId(usrprofileId);
    lc.setConvertedStatus('Qualified');

    Database.LeadConvertResult lcr = Database.convertLead(lc);
*/

list<Lead> l_lst = new list<Lead>();
l_lst = [SELECT IsUnreadByOwner__c from lead where id = : l.id];

PageReference pageRef = Page.massConvert;
Test.setCurrentPage(pageRef); 
pageRef.getParameters().put('id', l.id); 

CMassConvert cm = new CMassConvert();
cm.MassConvert(l_lst);

I am getting an error when I run the test class

System.DmlException: Insert failed. First exception on row 0; first error: FIELD_INTEGRITY_EXCEPTION, Converted Account empty for a Converted Lead.: [ConvertedAccountId]

I know I am missing out some thing but cannot identify what is the issue properly.