JUnit max/min values

Kindly clarify how would I test Bigdecimal max value from the Map values > I have initially used Object mapper to map Strings that contained date and rate for the specific currency so I would like to create a method that tests for max/min values also would be great to know the approach to test a LocalDate would be.

Thank you in advance

Map.Entry<LocalDate, BigDecimal> getMinRate(Response response) {
        return Collections.min(response.getBpi().entrySet(), Map.Entry.comparingByValue());
    }