php unit test code coverage with drive Pcov problems about function_exists

Question

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if (!function_exists('birthday_to_age')) {

/**
 * calculate the age of input date
 * @param Carbon $date input date
 * @return int the age
 */
function birthday_to_age(Carbon $date): int
{
    return floor((date('Ymd') - $date->format('Ymd')) / 10000);
}

}

if (!function_exists('log_http_client_response')) {

/**
 * Function log_http_client_response
 * @param Response $response
 * @param string $prefix
 * @param string $level
 */
function log_http_client_response(Response $response, string $prefix = '', string $level = 'debug')
{
    $content = $prefix . "Response http_status: {$response->status()}, http_headers: "
        . json_encode($response->headers()) . ", http_body: {$response->body()}";
    Log::$level($content);
}

}

The coverage report showed two lines of "if (!function_exists('function_name'))" were not been covered, but these two functions within "if" was covered. It's ridiculous because when I used xdebug to be as the driver, these two lines were covered, but when I changed the driver to pcov without any other changes, the problem occurred.

Did any one meet this problem? does any one know how to cover these two lines?

Thanks