Cache class for PHP

Cache.php

<?php                                                                           
class Cache {                                                                   
    private $cache = [];                                                        
                                                                          
    public function functionCall($callable, $params = []){                      
        $hash = serialize([$callable, $params]);                                
        if(!isset($this->cache[$hash])){                                        
            $this->cache[$hash] = call_user_func_array($callable, $params);     
            echo "Function called!\t";                                          
        }else{                                                                  
            echo "Cached result returned.\t";                                   
        }                                                                       
        return $this->cache[$hash];                                             
    }                                                                           
}                                                                               

// Tests for the caching functionality
$cache = new Cache();                                                           

function test($a, $b){                                                          
    sleep(1);                                                                   
    return $a + $b;                                                             
}      

echo $cache->functionCall('test', [1,1])."\n";                                  
echo $cache->functionCall('test', [1,2])."\n";                                  
echo $cache->functionCall('test', [1,3])."\n";                                  
echo $cache->functionCall('test', [1,1])."\n";                                  

class Foo {                                                                     
    public static function sum($a, $b){                                         
        sleep(1);                                                               
        return $a + $b;                                                         
    }                                                                           

    public function otherSum($a, $b){                                           
        sleep(1);                                                               
        return $a + $b;                                                         
    }                                                                           
}                                                                               

// Static call test                                                             
echo $cache->functionCall(['Foo', 'sum'], [1,1])."\n";                          
echo $cache->functionCall(['Foo', 'sum'], [1,2])."\n";                          
echo $cache->functionCall(['Foo', 'sum'], [1,3])."\n";                          
echo $cache->functionCall(['Foo', 'sum'], [1,1])."\n";                          

// Object call test                                                             
$foo = new Foo;                                                                 
echo $cache->functionCall([$foo, 'otherSum'], [1,1])."\n";                      
echo $cache->functionCall([$foo, 'otherSum'], [1,2])."\n";                      
echo $cache->functionCall([$foo, 'otherSum'], [1,3])."\n";                      
echo $cache->functionCall([$foo, 'otherSum'], [1,1])."\n";