<?php

$array = array(
   'Key1' => 'Test',
   'Key2' => 'BlahBlah',
);

$max_key_length = max(array_map('strlen', array_keys($array)));
$max_value_length = max(array_map('strlen', $array));

foreach($array as $key => $value) {
    echo sprintf("%-{$max_key_length}s   %{$max_value_length}s\n", $key, $value);
}

Key1       Test
Key2   BlahBlah