The Projects to Practice TDD.

This practice was designed from below

Greeting    String Calculater    Roman Numbers

Gained benefit of

1. The code looking good

For example, the romanToDecimal() method which converts Roman numeral into decimal is like below.

fun romanToDecimal(roman: String): Int {
    if (roman.isEmpty()) return 0
    return roman
        .toCharArray()
        .mapIndexed { i, c ->
            getSignOfCharacter(i, roman) * romanValue[c]!!
        }.sum()
}

fun getSignOfCharacter(i: Int, roman: String) =
    if (i < roman.indices.last && romanValue[roman[i]]!! < romanValue[roman[i + 1]]!!) -1 else 1

And this is the code doing exactly the same without TDD

fun romanToDecimal(roman: String): Int {
    var sum = 0
    for (i in roman.indices.first until roman.indices.last) {
        val cur = roman[i]
        val next = roman[i + 1]
        if (cur == 'I' && (next == 'V' || next == 'X'))
            sum -= 2 * romanValue['I']!!
        if (cur == 'X' && (next == 'L' || next == 'C'))
            sum -= 2 * romanValue['X']!!
        if (cur == 'C' && (next == 'D' || next == 'M'))
            sum -= 2 * romanValue['C']!!
    }
    for (c in roman.toCharArray()) {
        sum += romanValue[c]!!
    }
    return sum
}

The former code looks simpler and is easier to understand developer's intention.

2. The code being safer.

Among the TDD practice projects I've implemented,
the average production code is 21.6 lines, whereas the test code is 43.6 lines.
This lessons the vulnerability of malfunction.
And the test has higher quality than of made after implementing production codes.