I have a following apex Class for which I need to create a test class

public class GenerateFirstInvoices {
    @InvocableMethod
    public static void fetchOrderItems(List<Id> orderId) {
        List<OrderItem> oproduct = [SELECT Id, OrderId, Next_Billing_Date__c, OriginalOrderItemId, Payment_Term__c, Quantity, Remaining_Amount__c, Contact_Name__c, Contact_Address__c, Contact_Email__c, Contact_Number__c, Trn_Number__c, CRM_Number__c, FAR_or_HHS__c, Description, Created_Date__c FROM OrderItem WHERE OrderId = :orderId];
        Proforma_Invoice__c[] recordsToInsert = new Proforma_Invoice__c[0];
        Map<String, Integer> factors = new Map<String, Integer> {
            'Monthly' => 11,
            '2 Months' => 5,
            'Quarterly' => 3,
            '25%' => 3,
            'Semi Annually' => 1,
            '50%' => 1
        };
        for (OrderItem oitem : oproduct) {
            Integer factor = factors.get(oitem.Payment_Term__c);
            Integer DateInterval = 0;
            for (Integer i = 1; i <= factor; i++) {
                if (factor == 11) {
                    DateInterval = DateInterval + 30;
                } else if (factor == 5) {
                    DateInterval = DateInterval + 60;
                } else if (factor == 3) {
                    DateInterval = DateInterval + 90;
                } else if (factor == 1) {
                    DateInterval = DateInterval + 180;
                } else {
                    DateInterval = DateInterval;
                }
                recordsToInsert.add(new Proforma_Invoice__c(
                    Order__c = oitem.OrderId,
                    Order_Product__c = oitem.Id,
                    Rate__c = oitem.Remaining_Amount__c / factor,
                    Amount__c = oitem.Remaining_Amount__c / factor,
                    Expense_Budget__c = oitem.Remaining_Amount__c / factor,
                    Quantity__c = oitem.Quantity,
                    Status__c = 'Draft',
                    Paid_Status__c = 'No',
                    Contact_Name__c = oitem.Contact_Name__c,
                    Contact_Address__c = oitem.Contact_Address__c,
                    Contact_Email__c = oitem.Contact_Email__c,
                    Contact_Number__c = oitem.Contact_Number__c,
                    TRN_Number__c = oitem.TRN_Number__c,
                    FAR_or_HHS__c = oitem.FAR_or_HHS__c,
                    CRM_No__c = oitem.CRM_Number__c,
                    Created_Date__c = oitem.Created_Date__c + DateInterval
                ));
            }
        }
        insert recordsToInsert;
    }
}

Following is my test class with only 29% code coverage

@isTest
private class GenerateFirstInvoicesTEST {
    @isTest
    private static void fetchOrderItemsTEST() {
        String Payment_Terms = 'Monthly';
        Database.SaveResult dsr;
        OrderItem drOrderItem;
        drOrderItem=new OrderItem(OrderId='802x00000000000AAA',PricebookEntryId='802x00000000000AAA',Quantity=123,Payment_Term__c='Monthly',type__c='Subscription');
        dsr=Database.insert(drOrderItem,false);
        
        Test.startTest();
        try{
        GenerateFirstInvoices.fetchOrderItems(new List<Id>{dsr.getId()});
        }catch(Exception e){}
        try{
        GenerateFirstInvoices.fetchOrderItems(null);
        }catch(Exception e){}
        Test.stopTest();
        
        Test.startTest();
        try{
                //drOrderItem.Payment_Term__c == 'Monthly';
                Proforma_Invoice__c proforma = new Proforma_Invoice__c();            
                proforma.Rate__c = 100;
                proforma.Amount__c = 100;
                proforma.Order_Product__c = '802x00000000000AAA';
                proforma.Quantity__c = 1;
        
                insert proforma;
            
        }catch(Exception e){}
        Test.stopTest();
    }
    @isTest
    private static void GenerateFirstInvoicesTEST(){
        GenerateFirstInvoices obj = new GenerateFirstInvoices();
    }
}

Can anyone please help me create a test class for my apex class & guide me on how to get to the section inside loop using test code.

I have a following apex Class for which I need to create a test class

public class GenerateFirstInvoices {
    @InvocableMethod
    public static void fetchOrderItems(List<Id> orderId) {
        List<OrderItem> oproduct = [SELECT Id, OrderId, Next_Billing_Date__c, OriginalOrderItemId, Payment_Term__c, Quantity, Remaining_Amount__c, Contact_Name__c, Contact_Address__c, Contact_Email__c, Contact_Number__c, Trn_Number__c, CRM_Number__c, FAR_or_HHS__c, Description, Created_Date__c FROM OrderItem WHERE OrderId = :orderId];
        Proforma_Invoice__c[] recordsToInsert = new Proforma_Invoice__c[0];
        Map<String, Integer> factors = new Map<String, Integer> {
            'Monthly' => 11,
            '2 Months' => 5,
            'Quarterly' => 3,
            '25%' => 3,
            'Semi Annually' => 1,
            '50%' => 1
        };
        for (OrderItem oitem : oproduct) {
            Integer factor = factors.get(oitem.Payment_Term__c);
            Integer DateInterval = 0;
            for (Integer i = 1; i <= factor; i++) {
                if (factor == 11) {
                    DateInterval = DateInterval + 30;
                } else if (factor == 5) {
                    DateInterval = DateInterval + 60;
                } else if (factor == 3) {
                    DateInterval = DateInterval + 90;
                } else if (factor == 1) {
                    DateInterval = DateInterval + 180;
                } else {
                    DateInterval = DateInterval;
                }
                recordsToInsert.add(new Proforma_Invoice__c(
                    Order__c = oitem.OrderId,
                    Order_Product__c = oitem.Id,
                    Rate__c = oitem.Remaining_Amount__c / factor,
                    Amount__c = oitem.Remaining_Amount__c / factor,
                    Expense_Budget__c = oitem.Remaining_Amount__c / factor,
                    Quantity__c = oitem.Quantity,
                    Status__c = 'Draft',
                    Paid_Status__c = 'No',
                    Contact_Name__c = oitem.Contact_Name__c,
                    Contact_Address__c = oitem.Contact_Address__c,
                    Contact_Email__c = oitem.Contact_Email__c,
                    Contact_Number__c = oitem.Contact_Number__c,
                    TRN_Number__c = oitem.TRN_Number__c,
                    FAR_or_HHS__c = oitem.FAR_or_HHS__c,
                    CRM_No__c = oitem.CRM_Number__c,
                    Created_Date__c = oitem.Created_Date__c + DateInterval
                ));
            }
        }
        insert recordsToInsert;
    }
}

Following is my test class with only 29% code coverage

@isTest
private class GenerateFirstInvoicesTEST {
    @isTest
    private static void fetchOrderItemsTEST() {
        String Payment_Terms = 'Monthly';
        Database.SaveResult dsr;
        OrderItem drOrderItem;
        drOrderItem=new OrderItem(OrderId='802x00000000000AAA',PricebookEntryId='802x00000000000AAA',Quantity=123,Payment_Term__c='Monthly',type__c='Subscription');
        dsr=Database.insert(drOrderItem,false);
        
        Test.startTest();
        try{
        GenerateFirstInvoices.fetchOrderItems(new List<Id>{dsr.getId()});
        }catch(Exception e){}
        try{
        GenerateFirstInvoices.fetchOrderItems(null);
        }catch(Exception e){}
        Test.stopTest();
        
        Test.startTest();
        try{
                //drOrderItem.Payment_Term__c == 'Monthly';
                Proforma_Invoice__c proforma = new Proforma_Invoice__c();            
                proforma.Rate__c = 100;
                proforma.Amount__c = 100;
                proforma.Order_Product__c = '802x00000000000AAA';
                proforma.Quantity__c = 1;
        
                insert proforma;
            
        }catch(Exception e){}
        Test.stopTest();
    }
    @isTest
    private static void GenerateFirstInvoicesTEST(){
        GenerateFirstInvoices obj = new GenerateFirstInvoices();
    }
}

Can anyone please help me create a test class for my apex class & guide me on how to get to the section inside loop using test code.