I am having a super hard time in writing a test class. The extension lets a user select multiple records from child (Contingency__c) and add to the related list of parent (Billing_Change_form__c) where the account is the same. It contains a wrapper class. I have no idea how to get any coverage.
This is the test class that I have come up with so far:

@isTest
public class bcfTest {
   public static testMethod void adBill(){
        Billing_Change_form__c testBill = new Billing_Change_Form__c();
        testBill.Name = 'Test name';
        insert testBill;
        
       Billing_Change_form__c testBill2 = new Billing_Change_Form__c();
        testBill2.Name = 'Test name2';
        insert testBill2;
       
         Contingency__c caseTest = new Contingency__c();
        caseTest.Name = 'test Case';
        caseTest.Contingency__c = 'IN BILLING';
        caseTest.VENDOR_INVOICE__r.Account_del__r.id='1234';
        insert caseTest;
        
       Contingency__c caseTest2 = new Contingency__c();
        caseTest2.Name = 'test Case2';
        caseTest2.Contingency__c = 'IN BILLING';
        caseTest2.VENDOR_INVOICE__r.Account_del__r.id='5678';
        insert caseTest2;
       
        Account accTest = new Account();
        accTest.Name = 'Test Account';
        insert accTest;
       
        Test.startTest();
       PageReference pageRef = Page.bcTest; // Add your VF page Name here
        pageRef.getParameters().put('id', String.valueOf(testBill.Id));
       Test.setCurrentPage(pageRef);
       
      
        List<wrapperCase> wrapList = new List<wrapperCase>();
        List<Contingency__c> selCase = new List<Contingency__c>();
        
       for(Contingency__c b : [Select id, name, 
                               contingency__c, VENDOR_INVOICE__r.Account_del__r.Id from Contingency__c
                               where (VENDOR_INVOICE__r.Account_del__r.Id = :accTest.Id) ]){
                                   wrapList.add(New wrapperCase(b));
                               }
       
       
       for(wrapperCase WATest: wrapList){
           WATest.check = true;
       }
       
           
        System.assertEquals(testBill.Id, caseTest.Bill_Form__c);
        System.assertEquals('Test name',testBill.Name);
        System.assertEquals('IN BILLING', caseTest.CONTINGENCY__c);
        
        test.stopTest();
    }
    public class wrapperCase{
        public contingency__c con{get;set;}
        public boolean check{get;set;}
        public wrapperCase(contingency__c c){
            con = c;
            check = false;           
        }
    }
}

My controller extension:
public with sharing class test2 {
    //Declare varialbles
    public string lookup{get;set;}
    public list<conCase> caseList{get;set;}
    public boolean allbool{get;set;}
    public string inputValue{get;set;}
    public boolean bool{get;set;}
    public set<id> caseIds{get;set;}
    Billing_Change_form__c[] accID = [Select account__c from Billing_Change_Form__c where 
                                               id = :System.currentPagereference().getParameters().get('id')];
    
    
    ApexPages.StandardController controller;
    
    //Constructor
    public test2(ApexPages.StandardController con){
        controller = con;
        caseList = new list<conCase>();
        bool = false;
        caseIds = new Set<id>();
    }


    //Event on clicking the checkbox
    public void inIt(){
        List<Contingency__c> selectedCase = new list<Contingency__c>();
        lookUp = '';
        for(conCase conObj : caseList){
            if(conObj.check != False){
                system.debug('conObj.con'+ conObj.con);
                selectedCase.add(conObj.con);
                lookUp += conObj.con.name + ', ';
                system.debug('lookup:'+ lookup);
                caseIds.add(conObj.con.id);
                bool = true;
            }
               If(conObj.check != true){
                caseIds.remove(conObj.con.id); }   
    }
    }

    //Displaying the records 
    public List<conCase> getShow(){
        caseList = new list <conCase> ();

        for(Contingency__c coObj : [Select id, name,billing_type__c, report_description__c, discovery_amount__c,
                        billing_begins_date__c, contingency__c, VENDOR_INVOICE__r.Account_del__r.Id from Contingency__c
            where (VENDOR_INVOICE__r.Account_del__r.Id = :accID[0].Account__c)  AND (Bill_form__c = null)])
                                 
        {
            caseList.add(new conCase(coObj, Bool));
        }
     
        return caseList;
    }
        
    //Event on saving the selected records
    public PageReference mySave(){
        list<Contingency__c> updateSelectedCase = new list<Contingency__c>();
        id billId = ApexPages.currentPage().getparameters().get('id');
        System.debug('Bill ID is' + billID);
        for(Contingency__c co:[select id, name, bill_form__c from Contingency__c where id = :caseIds ]){
            co.bill_form__c = billId;
            updateSelectedCase.add(co);
        }
        update updateSelectedCase;
        return null;
    }

    //Event When the cancel button is hit
    public void closePopup(){
        bool = false;
    }
    public void add(){
        bool = true;
    }
    
    //Wrapper class for the selected records
       public class conCase{
        public contingency__c con{get;set;}
        public boolean check{get;set;}
        public conCase(contingency__c c, boolean boo){
            con = c;
            check = boo;           
        }
    }
    
}

My visualforce Page:

<apex:page showHeader="False" standardController="Billing_Change_Form__c" extensions="test2">
  <script>
     function closeWindow(){      
            window.opener.location.href="/{!$CurrentPage.parameters.id}";
            window.top.close();
      }
    </script>
    
    <apex:form >
    <apex:PageBlock title="CaseFindings" id="counter">

                    <apex:pageBlockButtons >
                      <apex:commandButton value="Save" action="{!mySave}" onComplete="closeWindow();"/>   
                      <apex:commandButton value="Cancel" onclick="window.top.close();" immediate="true" action="{!closePopup}"/>  
                </apex:pageBlockButtons>

            <apex:pageBlockTable value="{!show}" var="e" title="show">
                
            <apex:column >
                <apex:inputCheckbox value="{!e.check}" />
    <apex:actionSupport event="onclick" action="{!inIt}" rerender="none"/>
                </apex:column>
                
                <apex:column value="{!e.con.Name}"/>
                <apex:column value="{!e.con.DISCOVERY_AMOUNT__c}"/>
                <apex:column value="{!e.con.BILLING_BEGINS_DATE__c}"/>
                <apex:column value="{!e.con.REPORT_DESCRIPTION__c}"/>
                <apex:column value="{!e.con.CONTINGENCY__c}"/>
            </apex:pageBlockTable>
        </apex:PageBlock>
    </apex:form>
</apex:page>


Hoping to get standard 75% coverage. If anyone can help me with it, I would really appreciate it! Thanks!