String extension that returns the best font size to fit certain size

FontSizeThatFits.swift

extension String {
    func fontSizeThatFitsWidth(size: CGSize, font: UIFont) -> CGFloat {
        let testString = self as NSString
        
        var fontSize: CGFloat = 100
        let minFontSize: CGFloat = 5
        
        while fontSize > minFontSize {
            let testFont = font.fontWithSize(fontSize)
            let textSize = testString.sizeWithAttributes([NSFontAttributeName : testFont])
            if textSize.width > size.width {
                fontSize -= 2
            } else {
                break
            }
        }
        
        return fontSize
    }
}