I'm having some trouble with a class I'm creating. The purpose of this class is to essentially work around the Analytical Snapshot limit by batching the job- which is all fine but i'm getting the error in the title. Here's the code

global with sharing class AUMSnapshot implements Database.Batchable<sObject> {
   global final String Query;

   global AUMSnapshot() {
        this.Query = 'Select a.Id, a.navmfv2__Latest_AUM__c, a.navmfv2__AUM_as_of__c, a.Value__c, a.Research__c, a.Balanced__c, a.Government_MM__c, a.Hickory__c, a.NE_Tax_Free__c, a.Partners_Value__c, a.PIII__c, a.Short_Intermediate_Classes_combined__c  From Account a';
   }
   
   global AUMSnapshot(String query) {
        this.Query = query;
   }

   global Database.QueryLocator start(Database.BatchableContext BC) {
      return Database.getQueryLocator(Query);
   }

   global void execute(Database.BatchableContext BC, List<sObject> scope) {
    
    List<Account> AccountAssets = (List<Account>) scope;
    
    List<Account> updateAccount = new List<Account>();
    
    for (Account AccountAsset : AccountAssets) {
	Historical_AUM__c haum = new Historical_AUM__c( Account__c = AccountAsset.Id, AUM__c = AccountAsset.navmfv2__Latest_AUM__c, Value__c = AccountAsset.Value__c, Research__c = AccountAsset.Research__c, Record_Date__c = AccountAsset.navmfv2__AUM_as_of__c, Balanced__c = AccountAsset.Balanced__c, Government_MM__c = ACcountAsset.Government_MM__c, NE_Tax_Free__c = AccountAsset.NE_Tax_Free__c, Hickory__c = AccountAsset.Hickory__c, Partners_Value__c = AccountAsset.Partners_Value__c, PIII__c = AccountAsset.PIII__c, Short_Intermediate__c = AccountAsset.Short_Intermediate_Classes_combined__c, UpsertID__c = AccountAssets.Id & AccountAsset.navmfv2__AUM_as_of__c);
	upsert haum UpsertID__c; 
	
    }
    
    update updateAccount;
    
   }

   global void finish(Database.BatchableContext BC){

   }
   
   public static testMethod void testBatch() {
    
    Account a = new Account(Name = 'Test Account', ShippingPostalCode = '00000', BillingCountry = 'US', navmfv2__AUM_as_of__c = Date.today());
    insert a;
    
	Historical_AUM__c b = new Historical_AUM__c( Account__c = a.Id, AUM__c = a.navmfv2__Latest_AUM__c, Value__c = a.Value__c, Research__c = a.Research__c, Record_Date__c = a.navmfv2__AUM_as_of__c, Balanced__c = a.Balanced__c, Government_MM__c = a.Government_MM__c, NE_Tax_Free__c = a.NE_Tax_Free__c, Hickory__c = a.Hickory__c, Partners_Value__c = a.Partners_Value__c, PIII__c = a.PIII__c, Short_Intermediate__c = a.Short_Intermediate_Classes_combined__c, UpsertID__c = a.Id & a.navmfv2__AUM_as_of__c);
	upsert b;

    Test.StartTest();
    AUMSnapshot BatchClass = new AUMSnapshot();
    Database.executeBatch(BatchClass, 1);
    //BatchClass.execute(null, new List<sObject>{zipper});
    Test.StopTest();
   }
}

 The part where I declare haum is the offending line of code. I would appreciate any help.