いまさらながらSwiftでTDDをやってみた ref: https://qiita.com/hmhmsh/items/842e795d4b2a41556b5b

Testable_swiftTests.swift

class TodoList {
    var list = Array<String>()

    func isEmpty() -> Bool {
        return list.count == 0
    }

    func append(_ todo: String) {
        list.append(todo)
    }

    func getTop() throws -> String {
        do {
            try emptyCheck()
        }
        return list[0]
    }

    func size() -> Int {
        return list.count
    }

    func removeTop() throws {
        do {
            try emptyCheck()
        }
        list.remove(at: 0)
    }

    func emptyCheck() throws {
        if isEmpty() {
            throw NSError(domain: "error", code: -1, userInfo: nil)
        }
    }
}

TodoList.swift

class TodoList {
    var list = Array<String>()

    func isEmpty() -> Bool {
        return list.count == 0
    }

    func append(_ todo: String) {
        list.append(todo)
    }

    func getTop() throws -> String {
        do {
            try emptyCheck()
        }
        return list[0]
    }

    func size() -> Int {
        return list.count
    }

    func removeTop() throws {
        do {
            try emptyCheck()
        }
        list.remove(at: 0)
    }

    func emptyCheck() throws {
        if isEmpty() {
            throw NSError(domain: "error", code: -1, userInfo: nil)
        }
    }
}