Added duplicate td for existing table using jQuery

Question

I am trying to add a td for existing table using jQuery. But it's adding duplicate. How to validate exactly to add the td.

I have tried below code:

<table>
<thead>
<tr>
    <th>head1</th>
    <th>head2</th>
    <th>head3</th>
    <th>head4</th>
</tr>
</thead>
    <tbody>
        <tr >
            <td class="test test2">a1</td>
            <td>a2</td>
            <td>a3</td>
        </tr>
        <tr>
            <td class="test">c1</td>
            <td>c2</td>
            <td>c3</td>
        </tr>            
    </tbody>
</table>

jQuery code

 <script>
       $(document).ready(function() {

       for(i=0;i<2;i++){
         var row = '<td style="background: red">b_'+ i +'</td>';    
                $('[class="test"]').before(row);
       }

})
        </script>

I want to add a td where exactly match the class="test" is, but it's adding both class="test test2" and class="test".

How can I do this?

Answer 1

tested and working

$(document).ready(function() {

       for(i=0;i<2;i++){
         var row = '<td style="background: red">b_'+ i +'</td>';    
                $('.test').before(row);
       }

})

other solution

 $(document).ready(function() { var i=1;
    $(".test").each(function() { 
   if(i!=1) {
    var row = '<td style="background: red">b_'+ i +'</td>';    
                    $(this).before(row);
    }
                    i=i+1;
})  });