Hi 

I am new to writting apex for integration. I have written the logic and it's working fine. Can someone please help me to write test class the below class as I am unable to do so. I have tried multiple times but the class is not getting covered.

@RestResource(urlMapping='/AccountBiilingDate/*')
global class AccountBiilingDateUpdateClass{
    @HttpPost 
    global static List<ResponseWrapper> updateAccBillDate(){
        RestRequest accBillDateRequest = RestContext.request;
        String jsonResponse = '';
        RestResponse res = RestContext.response;
        
        String requestBody = accBillDateRequest.requestBody.toString();
        
        List<AccountBiilingDate> accRecsReceived = (List<AccountBiilingDate>) JSON.deserialize(requestBody, List<AccountBiilingDate>.class);
        List<ResponseWrapper> wrperlist = new List<ResponseWrapper>();
        List<Account> accListToUpdt = new List<Account>();
        Set<Account> accSetToUpdate = new Set<Account>();
        
        for(AccountBiilingDate accBillDate : accRecsReceived){
            Account acc = new Account();
            acc.Id = Id.valueOf(accBillDate.ACC_ID);
            If(accBillDate.BILLDATE != ''){
                acc.Billing_Date__c = Date.valueOf(accBillDate.BILLDATE);
            }else{
                acc.Billing_Date__c = NULL;
            } 
            accSetToUpdate.add(acc);
        }
        accListToUpdt .addALL(accSetToUpdate);
    
        
        Database.SaveResult[] srList = database.update(accListToUpdt,false);
        
        for (Database.SaveResult sr : srList){
            if (sr.isSuccess()){
                jsonResponse = 'Successfully updated';
                res.responseBody = blob.valueOf(jsonResponse);
                wrperlist.add(new ResponseWrapper(sr.getId(),jsonResponse,200));
            }else {
                for(Database.Error err : sr.getErrors()) {
                    res.responseBody = Blob.valueOf(err.getMessage());
                    wrperlist.add(new ResponseWrapper(sr.getId(),err.getMessage(),400));
                }
            }
        }
        return wrperlist;
    }
    global class AccountBiilingDate{
        public String ACC_ID;  //Account Id
        public String BILLDATE;  //yyyy-mm-dd format
    }
}

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global class ResponseWrapper{
    public String Id ;
    public string Status;
    public Integer Statuscode;
    public ResponseWrapper(String Id, String statusMsg,Integer statusCode){
        this.Id  = Id;
        this.Status = statusMsg;
        this.Statuscode = statusCode;
    }
    
}