File4.swift

public struct MockFunc<Input, Output> {
    public var parameters: [Input] = []
    public var result: (Input) -> Output = { _ in fatalError() }

    public mutating func callAndReturn(_ input: Input) -> Output {
	parameters.append(input)
        return result(input)
    }

    public mutating func returns(_ value: Output) {
        result = { _ in value }
    }
}