Refactoring form code in php

I get three values from a form (thread_title, thread_content and thread_tags):

This is the code to check their lengths:

$errors = array();

$thread_title = filter_input(INPUT_POST, 'thread_title');
$thread_content = filter_input(INPUT_POST, 'thread_content');
$thread_tags = filter_input(INPUT_POST, 'thread_tags');


if (strlen($thread_title) < 20 )
{
    $errors['thread_title'] = 'Title is too short, minimum is 20 characters.';    
}

if (strlen($thread_content) < 30 )
{
    $errors['thread_content'] = 'Content is too short, minimum is 30 characters.';
}

if (strlen($thread_tags) < 3)
{
    $errors['thread_tags'] = 'Tags must be atleast 3 characters.';
}

I repeat this in the reply.php file:

if (strlen($repl开发者_如何学运维y_content) < 20)
{
    $errors['reply_content'] = 'Reply must be atleast 20 characters.';
}

.etc

If the errors array is empty I then clean the data and submit it to the database. How can this code be made cleaner, refactored?

I know I can use something like PEAR QUICK_FORM (2.0?), however that is still in alpha and the error messages appear as a JS popup in that and not next to the required field.

github is a source of lot of really good code. I did a quick search for form validation. For example:

• https://github.com/bretticus/PHP-5.3-Form-Validator looks okay?

Furthermore I believe if you want to refactor your code, you should practice TDD(unit testing).