$S = new Calc();
$S->setOperation('5 - 5');
$S->run();
$S->getResult();
if ($S->getResult() == 0) {
    echo "Test subtraction 5 - 5 passed with result 0\n";
}
// multiply
$M = new Calc();
$M->setOperation('5 * 5');
$M->run();
if ($M->getResult() == 25) {
    echo "Test subtraction 5 * 5 passed with result 25\n";
}
// divide
$D = new Calc();
$D->setOperation('5 / 5');
$D->run();
if ($D->getResult() == 1) {
    echo "Test subtraction 5 / 5 passed with result 1\n";
}
// all the things
$X = new Calc();
$X->setOperation('5 * 5 - 4 / 2 + 7');
$X->run();
if ($X->getResult() == 30) {
    echo "Test 5 * 5 - 4 / 2 + 7 passed with result 30\n";
}
echo 'Running 5 * 5 - 4 / 2 + 7 as a static method Calc::exec() ..... returning: ';
echo Calc::exec('5 * 5 - 4 / 2 + 7');
echo "\n";