Testing date to hex string

//TODO: Write a test for the hex string -> UIColor conversion
func checkHexStringForDateString(dateString: String) {
    // given
    let changes: [String: String] = [
        "1" : "A",
        "2" : "B",
        "3" : "C",
        "4" : "D",
        "5" : "E",
        "6" : "F"
    ]
    var components = dateString.componentsSeparatedByString(" : ")
    for i in 0...(components.count - 1) {
        for (key, obj) in changes {
            components[i] = components[i].stringByReplacingOccurrencesOfString(key, withString: obj)
        }
    }
    let expected = "#".stringByAppendingString(components.joinWithSeparator(" : "))
    
    // when
    let result = model.hexStringFromDateString(dateString)
    
    // then
    XCTAssertEqual(result, expected)
}

func testHexStringForDateString_shouldReturnAppropriateHexString() {
    checkHexStringForDateString("#012345")
    checkHexStringForDateString("#FDE283")
    checkHexStringForDateString("#426ABC")
    checkHexStringForDateString("#5F3A9D")
    checkHexStringForDateString("#76CD92")
}