Swift - 单元测试私有(private)变量和方法

Question

我正在尝试测试一个类，但我对测试什么感到困惑。这是我要进行单元测试的类:

class CalculatorBrain {

    private var accumulator = 0.0

    func setOperand(operand: Double) {
        accumulator = operand
    }

    var result: Double {
        return accumulator
    }

    private var operations: Dictionary<String, Operation> = [
        "=" : .Equals,

        "π" : .Constant(M_PI),
        "e" : .Constant(M_E),

        "±" : .UnaryOperation({ (op1: Double) -> Double in return -op1 }),
        "√" : .UnaryOperation(sqrt ),
        "cos": .UnaryOperation(cos),

        "+" : .BinaryOperation({ (op1: Double, op2: Double) -> Double in return op1 + op2 }),
        "−" : .BinaryOperation({ (op1: Double, op2: Double) -> Double in return op1 - op2 }),
        "×" : .BinaryOperation({ (op1: Double, op2: Double) -> Double in return op1 * op2 }),
        "÷" : .BinaryOperation({ (op1: Double, op2: Double) -> Double in return op1 / op2 })
    ]

    private enum Operation {
        case Constant(Double)
        case UnaryOperation((Double) -> Double)
        case BinaryOperation((Double, Double) -> Double)
        case Equals
    }

    func performOperation(symbol: String) {
        if let operation = operations[symbol] {
            switch operation {
            case .Constant(let value):
                accumulator = value
            case .UnaryOperation(let function):
                accumulator = function(accumulator)
            case .BinaryOperation(let function):
                executePendingBinaryOperation()
                pendingBinaryOperation = PendingBinaryOperationInfo(binaryOperation: function, firstOperand: accumulator)
            case .Equals:
                executePendingBinaryOperation()
            }
        }
    }

    private var pendingBinaryOperation: PendingBinaryOperationInfo?

    private struct PendingBinaryOperationInfo {
        var binaryOperation: (Double, Double) -> Double
        var firstOperand: Double
    }

    private func executePendingBinaryOperation() {
        if let pending = pendingBinaryOperation {
            accumulator = pending.binaryOperation(pending.firstOperand, accumulator)
            pendingBinaryOperation = nil
        }
    }
}

对于上面的代码，什么是好的测试。

是否值得测试字典 operations 中的每个操作(+、-、*、/等)？

是否值得测试私有(private)方法？

Answer 1

您不能使用 @testable 测试 Swift 中的私有(private)方法。您只能测试标记为 internal 或 public 的方法。正如文档所说:

Note: @testable provides access only for “internal” functions; “private” declarations are not visible outside of their file even when using @testable.

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