我的任务是在夏令时和夏令时创建一个包含UTC偏移量的字符串（例如：UTC+1UTC+2或UTC+1UTC+1，如果某个地区没有DST）。我的函数如下所示：

extension TimeZone {
    public func utcOffset(for date: Date = Date()) -> String {
        var currentTimeOffest = self.secondsFromGMT(for: date)
        if isDaylightSavingTime() {
            currentTimeOffest -= Int(daylightSavingTimeOffset(for: date))
        }
        let currentInHours = Int(currentTimeOffest / 3_600)
        let hoursSymbol: String = currentInHours > 0 ? "+" : ""

        let daylightOffset = TimeInterval(currentTimeOffest) + self.daylightSavingTimeOffset(for: date)
        let daylightInHours = Int(daylightOffset / 3_600)
        let daylightSymbol: String = daylightInHours > 0 ? "+" : ""

        return "UTC\(hoursSymbol)\(currentInHours)UTC\(daylightSymbol)\(daylightInHours)"
    }
}

它运行良好，我已经为此进行了测试。一切都很好，但是在多个国家/地区最近更改夏令时之后，即使我通过了一个特定的日期来计算以下项的偏移量，测试也开始失败：

    func testUtcOffset() {
        let date: Date = Date(timeIntervalSince1970: 1_557_482_400) //May 10,2019 10:00:00 AM

        let warsaw = TimeZone.init(identifier: "Europe/Warsaw")! //eastern hemisphere,with DST
        XCTAssertEqual(warsaw.utcOffset(for: date),"UTC+2UTC+3")

        let shanghai = TimeZone.init(identifier: "Asia/Shanghai")! //eastern hemisphere,without DST
        XCTAssertEqual(shanghai.utcOffset(for: date),"UTC+8UTC+8")

        let barbados = TimeZone.init(identifier: "America/Barbados")! //western hemisphere,without DST
        XCTAssertEqual(barbados.utcOffset(for: date),"UTC-4UTC-4")

        let bermuda = TimeZone.init(identifier: "Atlantic/bermuda")! //western hemisphere,with DST
        XCTAssertEqual(bermuda.utcOffset(for: date),"UTC-4UTC-3")

        let gmt = TimeZone.init(identifier: "GMT")! //GMT,without DST
        XCTAssertEqual(gmt.utcOffset(for: date),"UTC0UTC0")

        let lisbon = TimeZone.init(identifier: "Europe/Lisbon")! //GMT,with DST
        XCTAssertEqual(lisbon.utcOffset(for: date),"UTC+1UTC+2")
    }

2周前，warsaw和lisbon时区开始失败，今天bermuda。任何想法可能有什么问题吗？