Trouble getting any coverage on my test code to cover anything. 

It is a simple Visualforce page of fields already on the Pagelayout but to make it easier for the users.  
The button is on the Account Record and just pulls up the fields the sales team needs to fill out. 

Here is my Apex:
public with sharing class US_Medical_sales_mandatory {
    
    private ApexPages.StandardController c;

  
     public string getAccountId{get;set;}
       
      public US_Medical_sales_mandatory (ApexPages.StandardController controller)
      {
       
          getAccountid = ApexPages.CurrentPage().getparameters().get('ID');
      }
    

    
 public pagereference US_Medical_Sales_Mandatory()
 {

// you can fetch dummy lookup field value here and process accordingly.
  System.debug('@@@@@@@@@@@'+account.ownerid);
  return null;
 } 
}

Here is my test script:
@isTest
public class US_Medical_sales_mandatory_Test {
  
    Static testMethod void US_Medical_sales_mandatory_Test() {
     
         
        Account a = new Account(
            Name = 'testaccount'           );
        insert a;

      Account newAccount = new Account();
        
     Account acc= [Select ID,Name From Account WHERE Name='testaccount'];
      a.Id=acc.Id;
        a.AERs_in_Dept1__c = 'Manual';
        a.AER_s_in_Dept_2__c = 'Cantel ADV + 2.0';
        a.AER_s_in_Dept_3__c = 'Cantel ADV PT';
         a.AER_s_in_Dept_4__c = 'EVOTECH';
         a.AER_s_in_Dept_5__c = 'Cantel ISA';
         a.AER_s_in_Dept_6__c = 'Cantel ISA';
         a.Average_Numbers_of_Rooms__c = 45;
         a.Brush_Brand__c = 'Pull Thru';
         a.Colon_Volume_Yearly__c = 25;
         a.Department_AER_1__c = 'ENT';
         a.Department_AER_2__c =  'GI';
         a.Department_AER_3__c = 'GI';
         a.Department_AER_4__c = 'GI';
         a.Department_AER_5__c = 'GI';
         a.Department_AER_6__c = 'SPD';
          a.Disposable_Irrigation_Tubing__c =
         a.Disposable_Valves__c = 'Defendo';
         a.EGD_Volume_Yearly__c = 26;
         a.ERCP_Volume_Yearly__c = 26;
         a.EUS_Volume_Yearly__c= 27;
         a.QTY_of_AER_in_Dept_1__c= 78 ;
         a.QTY_of_AER_in_Dept_2__c= 1;
         a.QTY_of_AER_in_Dept_3__c= 1000;
         a.QTY_of_AER_in_Dept_4__c=14;
         a.QTY_of_AER_in_Dept_5__c=8;
 
        
        Test.startTest();
       Update a;
        Test.stopTest();
       
        PageReference ref = Page.US_MEDICAL_SALES_Mandatory;
        test.setCurrentPage(ref); 
            }
}