当在Codable中进行日期比较时，如何解决单元测试中的错误 [英] How to resolve error in unit testing when we have Date comparison in Codable

问题描述

我尝试使用 Codable 在json解码中使用自定义日期策略，如 https://stackoverflow.com/a/28016692/3477974 。这是简化的实现代码：

I tried to use custom date strategy in json decoding using Codable as describe in https://stackoverflow.com/a/28016692/3477974 . Here is the simplified implementation code:

public extension Formatter {
    static let iso8601: DateFormatter = {
        let formatter = DateFormatter()
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
        return formatter
    }()
}

public extension Date {
    var iso8601: String {
        return Formatter.iso8601.string(from: self)
    }
}


public extension JSONDecoder.DateDecodingStrategy {
    static let iso8601withFractionalSeconds = custom {
        let container = try $0.singleValueContainer()
        let string = try container.decode(String.self)
        guard let date = Formatter.iso8601.date(from: string) else {
            throw DecodingError.dataCorruptedError(in: container,
                  debugDescription: "Invalid date: " + string)
        }
        return date
    }
}


public extension JSONEncoder.DateEncodingStrategy {
    static let iso8601withFractionalSeconds = custom {
        var container = $1.singleValueContainer()
        try container.encode(Formatter.iso8601.string(from: $0))
    }
}

但是，关于单元测试它失败，尽管错误消息显示描述的日期方法使用的值相等：

However, when it comes to unit testing it fails although the error message shows equal value used by description method of date:

    func test_jsonCodable_iso8601() {
        let dates = [Date()] // ["Feb 9, 2020 at 12:55:24 PM"]

        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601withFractionalSeconds
        let data = try! encoder.encode(dates)

        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .iso8601withFractionalSeconds
        let decodedDates = try! decoder.decode([Date].self, from: data) // ["Feb 9, 2020 at 12:55:24 PM"]

        XCTAssertEqual(dates, decodedDates)
        // fails with error message: [2020-02-09 12:55:24 +0000]") is not equal to ("[2020-02-09 12:55:24 +0000]"
    }

您是否知道问题是什么以及如何解决？

Do you have any idea what is the issue and how we can resolve it?

顺便说一下，实际的可解码对象是以下类型，其中 publishedAt 的类型为date：

By the way, the actual decodable object is the following one where publishedAt is of type date:

public struct NewsItem: Equatable {
    public let id: UUID
    public let author: String
    public let title: String
    public let description: String
    public let urlToImage: URL?
    public let publishedAt: Date
    public let content: String

    public init(id: UUID,
                author: String,
                title: String,
                description: String,
                urlToImage: URL?,
                publishedAt: Date,
                content: String) {

        self.id = id
        self.author = author
        self.title = title
        self.description = description
        self.urlToImage = urlToImage
        self.publishedAt = publishedAt
        self.content = content
    }
}

extension NewsItem: Decodable {}

推荐答案

您要测试的是日期/ string转换，因此无需为此进行JSON编码和解码。以字符串形式的固定日期开始，将其转换为日期，然后返回并检查最终结果与固定日期

What you are testing is the date/string conversion so there is no need to involve JSON encoding and decoding into this. Start with a fixed date in string form, convert it to date and back and check the end result vs the fixed date

let input = "2020-02-02T19:10:23.123Z"

let formatter = DateFormatter.iso8601
let date = formatter.date(from: input)
let output = date?.iso8601

print(date != nil && input == output!)

请注意，这是在操场上编写的，而不是作为单元测试编写的

Note that this was written in a playground and not as a unit test

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