I need help writing a test class for my apex code. I really don't know much about apex. But I was able to create a visualforce page and an apex class that extends the standard controller. Everything works perfectly in my sandbox. But I have no idea how to write the test class so that I can push my code into production.

Here is my code for the visualforce page:

<apex:page standardController="WorkOrder" extensions="WorkOrderLineItemsOnWorkOrderClass">     

    <apex:sectionHeader title="Equipment on quote number {! WorkOrder.Workorder_Name__c } for {! WorkOrder.Account.Name }"/>
  
    <p></p>
    
    <apex:pageblock id="WorkOrderLineItemList"> 

         <br/> 

            <apex:pageBlockTable value="{!WorkOrderLineItems}" var="item">                          

                <apex:column value="{!item.Product_Code_Display__c}"/>
                
                <apex:column value="{!item.Description}"/> 
                
                <apex:column value="{!item.Quote_Line_Quantity_Display__c}"/>
                
                <apex:column value="{!item.Quote_Line_Net_Total_Display__c}"/> 
                
                <apex:column value="{!item.Group_Name__c}"/>
               
            </apex:pageBlockTable>     
            
     </apex:pageblock> 

</apex:page>

And here my code for my apex class that extends the standard controller:

public class WorkOrderLineItemsOnWorkOrderClass {

    public List<WorkOrderLineItem> WorkOrderLineItems{get;set;}

    public WorkOrder WorkOrders {get;set;} 

    public WorkOrder wo {get;set;} 

     //Constructor 

    public WorkOrderLineItemsOnWorkOrderClass(ApexPages.StandardController controller) { 

        wo = (WorkOrder)controller.getRecord();      

        WorkOrders = [SELECT id FROM WorkOrder WHERE id=: wo.id LIMIT 1]; 

        WorkOrderLineItems = [SELECT id,Group_Name__c,Product_Code_Display__c,Quote_Line_Quantity_Display__c, Description, Quote_Line_Net_Total_Display__c FROM WorkOrderLineItem WHERE WorkOrderid = :WorkOrders.id ORDER BY Quote_Line__c];     

} 
   
}