[SalesForce] tell how many records in a Database.QueryLocator()

You can't query more than 50,000 rows in your start method. You need a QueryLocator. In practice, this probably means you'll need to run your batch twice, once by accounts and then once by contacts. Probably something like this:

public class ProcessRecords implements Database.Batchable<SObject> {
    public String[] queries = new String[] { 'select brand__c from account', 'select brand__c from contact' };
    public Database.QueryLocator start(Database.BatchableContext context) {
        return Database.getQueryLocator(queries.remove(0));
    }
    public void execute(Database.BatchableContext context, SObject[] records) {
    // Do processing here
    }
    public void finish(Database.BatchableContext context) {
       if(!queries.isEmpty()) {
          Database.executeBatch(this, 20);
       }
    }
}

For unit testing, you may need to call your methods directly instead of trying to execute the batches using Test.stopTest(), to avoid chaining errors.

Some things to do:

1. Have your batch class implement Database.stateful
2. Declare some variables that are initialized in the constructor to 0. These variables count successes and errors; also a string variable that remembers the records that failed and why (initialized to empty string).
3. Use Database.update with allOrNothing = false instead of update within execute(). Interrogate each member of Database.SaveResult[] for isSuccess() and count succcesses and failures in your stateful variables from #2. Log in the stateful variable all the errors (id of record, name of record, and error message/exception)
4. In the finish method, send an email to the sysad of count of successes/failures + string variable of all the failures.
5. In finish() method, write your batch results to a custom Log__c record(s)