Avoiding Mixed DML Errors in Salesforce Batch Apex Classes

apex
public class MyBatchClass implements Database.Batchable<SObject> {
    
    public Database.QueryLocator start(Database.BatchableContext BC) {
        return Database.getQueryLocator('SELECT Id, Name FROM Account');
    }
    
    public void execute(Database.BatchableContext BC, List<SObject> scope) {
        // Process and update non-setup objects
        List<Account> accountsToUpdate = new List<Account>();
        for(SObject s : scope) {
            Account acc = (Account)s;
            acc.Description = 'Updated by batch';
            accountsToUpdate.add(acc);
        }
        update accountsToUpdate;
        
        // Call future method for setup objects
        if(!accountsToUpdate.isEmpty()) {
            updateSetupObjects(JSON.serialize(accountsToUpdate));
        }
    }
    
    @future
    public static void updateSetupObjects(String serializedData) {
        // Deserialize data if needed
        List<Account> accounts = (List<Account>)JSON.deserialize(serializedData, List<Account>.class);
        
        // Perform DML on setup objects
        User userToUpdate = [SELECT Id FROM User WHERE Id = :UserInfo.getUserId() LIMIT 1];
        userToUpdate.Title = 'Updated by batch';
        update userToUpdate;
    }
    
    public void finish(Database.BatchableContext BC) {
        // Perform any post-processing
    }
}

apex
public class NonSetupBatch implements Database.Batchable<SObject> {
    
    public Database.QueryLocator start(Database.BatchableContext BC) {
        return Database.getQueryLocator('SELECT Id, Name FROM Account');
    }
    
    public void execute(Database.BatchableContext BC, List<SObject> scope) {
        // Process non-setup objects only
        update scope;
    }
    
    public void finish(Database.BatchableContext BC) {
        // Start the batch for setup objects
        Database.executeBatch(new SetupBatch());
    }
}

public class SetupBatch implements Database.Batchable<SObject> {
    
    public Database.QueryLocator start(Database.BatchableContext BC) {
        return Database.getQueryLocator('SELECT Id FROM User LIMIT 10');
    }
    
    public void execute(Database.BatchableContext BC, List<SObject> scope) {
        // Process setup objects only
        List<User> users = (List<User>)scope;
        // update users
    }
    
    public void finish(Database.BatchableContext BC) {
        // Completion logic
    }
}

apex
@isTest
static void testBatchProcess() {
    // Create and process non-setup objects
    Account acc = new Account(Name = 'Test Account');
    insert acc;
    
    // Use runAs for setup objects
    User u = createTestUser();
    System.runAs(u) {
        // Perform operations on setup objects
        Profile p = [SELECT Id FROM Profile WHERE Name = 'Standard User'];
        User newUser = new User(/*...user fields...*/);
        insert newUser;
    }
    
    // Start your batch
    Test.startTest();
    Database.executeBatch(new MyBatchClass());
    Test.stopTest();
    
    // Assert results
}