gistfile1.txt

Assumptions: 

I will need to guard against an empty string. I will need to ignore anything that is not a letter.

Test Cases:

1. AbCdE
2. Fat Cat
3. "Ft6lKI9 !m"

Approach:
I know that there is a method in Javascript that turns a string into an array of its characters. I will use documentation to
look for a similar method. If I can do that, then I will simply loop through each index of the array and so long as the index
contains a letter I will use a ternary statement to see if it is lowercased. If it is then I will change it to uppercase, if
it isn't then I will change it to lowercase. I  will then join the array together back into a string and return the string.

Code:
func reversedCase(string: String) -> String {
    
    var newArray : [String] = []
    guard string != "" else {return ""}
    
    for character in string {
        let lowercasedCharacter = String(character).lowercased()
        String(character) == lowercasedCharacter ? newArray.append(String(character).uppercased()) : newArray.append(String(character).lowercased())
        }
    return newArray.joined()
    }