Add parse() from a json string to any Decodable

testDecodableExtensions.swift

import XCTest

extension Decodable {
    init(_ json: String) throws {
        self = try JSONDecoder().decode(Self.self, from: json.data(using: .utf8)!)
    }
}

final class DecodableExtensions: XCTestCase {

    struct Dummy: Codable {
        let text: String
        let number: Double
    }

    func testParse() throws {
        let json = #"{"text": "someString", "number": 123.45}"#
        let dummy = try Dummy(json)
        XCTAssertEqual(dummy.text, "someString")
        XCTAssertEqual(dummy.number, 123.45)
    }
}