create a file with this content and execute it:
<?php

xdebug_start_code_coverage();

function whatAmI($var) {
if (is_string($var)) {
return 'string';
} elseif ($var instanceof \stdClass) {
return '\stdClass';
} elseif (is_scalar($var)) {
return 'scalar';
}
return 'dunno!';
}

whatAmI(new \stdClass);
whatAmI(123);
whatAmI('string');
whatAmI(new DateTime());

var_dump(xdebug_get_code_coverage());