Drupal commerce, currency resolver, quickly change currency

If you are using currency resolver module in d8 you might need to change resolved currency quickly go to

namespace Drupal\commerce_currency_resolver;

and in getCurrency method, put 

$this->currency[$request] = "EUR";

for example, to get EUR currency in your checkout.

To quickly change/simulate IP of the user go to same namespace, check CurrencyHelper class and fing getUserCountry method, in there, before return you can enforce your own abbreviation like

    $country = "GB";

    return $country;

and you will enforce custom country IP.