如何在html选项标签中添加php？

I want to add values in option tag from sql database with the help of php. I have tried it but it is not showing anything
Here is my code which I have tried

<form action="addsubcategory.php" method="post">

        <input type="text" name="sub_category" placeholder="Add sub category">
<?php
        $res = mysqli_query($conn, "SELECT * FROM product_category");
echo '<select name="testSelect" id="testId">';

//Here is the problem

while ($record = mysqli_fetch_array($res)) {
echo '<option value="'.$record['category_name'].'">' .  "</option";
}
echo '</select>';
?>
 </form>

Try with

   echo '<option value="'.$record['category_name'].'">'.$record['category_name'].' "</option">';

Where you have this:

echo '<option value="'.$record['category_name'].'">' .  "</option";

You need this:

echo '<option value="'.$record['category_name'].'">' .  "</option>";

You have only added value to option tag.

while ($record = mysqli_fetch_array($res)) {
echo '<option value="'.$record['category_name'].'">' .  "</option";
}

instead of above code you should use:

       while ($record = mysqli_fetch_array($res)) {
    echo '<option value='.$record["category_name"].'>'. $record["category_name"] .'</option>';
}

Now above code will add value and text in option tag. Text to view and value to set or get value from db.