Can anyone help me to implement function and design test cases for this specification ?

def exchange(src, dst, amt): """ Returns the amount of currency received in the given exchange.

In this exchange, the user is changing amt money in currency src to the currency dst. The value returned represents the amount in currency currency_to.

The value returned has type float.

Parameter src: the currency on hand Precondition src is a string for a valid currency code

Parameter dst: the currency to convert to Precondition dst is a string for a valid currency code

Parameter amt: amount of currency to convert Precondition amt is a float or int """ pass