JSON_assertion_helper.swift

typealias JSON = [String: Any]
/// Helper for getting value from nested json dictionary
extension JSON {
    /// Get the value of the given keypath.
    /// - Parameter Path: The keypath separated by "."
    /// - Returns: The value of the specified keypath. Return `nil` if the value is not found.
    public subscript<T>(path path: String) -> T? {
        get {
            var dic: JSON? = self
            let keyPaths = path.split(separator: ".").map { String($0) }
            for (i, key) in keyPaths.enumerated() where dic != nil {
                if let target = dic?[key] as? T, i == (keyPaths.count - 1) {
                    return target
                }
                dic = dic?[key] as? JSON
            }
            return nil
        }
    }
}


// ======= Usage =======

/*
let jsonString = """
{
    "nestedKey": {
        "firstLevelKey": "firstLevelValue",
        "secondNestedKey": {
            "secondLevelKey": "secondLevelValue"
        }
    }
}
"""

// Object to be tested
let objectToTest = JSONDecoder().decode(StructToTest.self, from: data)

// Anser to the test
let jsonFact = JSONSerialization.jsonObject(with: data, options: .allowFragments)

// Result should be equal to the json fact
XCTAssertEqual(jsonFact[path: "nestedKey.secondNestedKey.secondLevelKey"],
               objectToTest.secondLevelValue)

*/