Expand test coverage and improve transaction management code.

app/Repositories/Currency/CurrencyRepositoryInterface.php

@@ -34,6 +34,12 @@ use Illuminate\Support\Collection;
  */
 interface CurrencyRepositoryInterface
 {
+    /**
+     * @param string $search
+     * @return Collection
+     */
+    public function searchCurrency(string $search): Collection;
+
     /**
      * @param TransactionCurrency $currency
      *