Fatal Error

i met this error in my local site Fatal error: Uncaught Error: Call to a member function get_cart() on null in , i have used this code

function test_cart( $id ){

$product_id = test_id( $course_id );

if ( $product_id > 0 ) {

$product = wc_get_product( $product_id );

foreach( WC()->cart->get_cart() as $cart_item_key => $values ) {

$cart_product = $values[‘data’];
if( $product_id == $cart_product->get_id() ) {

return true;

}

}

}

return false;

}