Swift Date Extension

Date.swift

import Foundation

extension Date {

    func formatted(
        components: [FormatterComponent]
    ) -> String {
        let dateFormatter = DateFormatter()
        var dateFormat: String = ""
        for (index, component) in components.enumerated() {
            dateFormat = index == .zero ?
                component.rawValue :
                dateFormat + component.rawValue
        }
        dateFormatter.dateFormat = dateFormat
        return dateFormatter.string(from: self)
    }

    enum FormatterComponent: String, CaseIterable {
        case dayOfMonth = "d"
        case dayOfMonthPadding = "dd"
        case dayOfWeekInMonth = "F"
        case dayOfWeekAbbreviationName = "E"
        case dayOfWeekWideName = "EEEE"
        case dayOfWeekNarrowName = "EEEEE"
        case dayOfWeekShortName = "EEEEEE"
        case monthOfYearSingle = "M"
        case monthOfYearDouble = "MM"
        case monthOfYearShorthandName = "MMM"
        case monthOfYearFullName = "MMMM"
        case monthOfYearNarrowName = "MMMMM"
        case yearFullDigits = "yyyy"
        case yearTwoDigits = "yy"
        case hour12 = "h"
        case hour12Padding = "hh"
        case hour24 = "H"
        case hour24Padding = "HH"
        case meridiem = "a"
        case minute = "m"
        case minutePadding = "mm"
        case second = "s"
        case secondPadding = "ss"
        case millisecond = "SSS"
        case dash = "-"
        case dot = "."
        case colon = ":"
        case comma = ","
        case underscore = "_"
        case whitespace = " "
    }
    
}

DateTests.swift

import XCTest
@testable import {your_project_name}

final class DateTests: XCTestCase {

    func testFormattedDate_whenFormatterComponentFilled_thenResultIsCorrect() {
        // Given
        // Timestamp is Saturday, September 12, 2020 2:21:24 PM GMT+07:00
        let now = Date(timeIntervalSince1970: 1599895284)

        // When
        let formatted = now.formatted(
            components: [
                .dayOfWeekAbbreviationName,
                .whitespace,
                .dayOfMonth,
                .comma,
                .whitespace,
                .monthOfYearFullName,
                .whitespace,
                .yearFullDigits,
                .whitespace,
                .hour12Padding,
                .colon,
                .minutePadding,
                .whitespace,
                .meridiem
            ]
        )

        // Then
        let expressionResult = formatted
        let expectedExpressionResult = "Sat 12, September 2020 02:21 PM"
        XCTAssertEqual(expressionResult, expectedExpressionResult)
    }

}