Adapt round-trip foreigner member test

Mirrors mapbox/turf-swift#175

Author: nighthawk

Tests/GeoJSONKitTests/ForeignMemberTest.swift

@@ -0,0 +1,59 @@
+//
+//  ForeignMemberTest.swift
+//  
+//
+//  Created by Adrian Schönig on 1/6/2022.
+//
+
+import Foundation
+
+import XCTest
+
+@testable import GeoJSONKit
+
+@available(iOS 10.0, *)
+class ForeignMemberTest: XCTestCase {
+  
+  func testForeignMemberCoding(in geoJSON: GeoJSON) throws {
+    let today = ISO8601DateFormatter().string(from: Date())
+    
+    var json = geoJSON.toJSON()
+    
+    // Convert the GeoJSON object to valid GeoJSON-T <https://github.com/kgeographer/geojson-t/>.
+    XCTAssert(json["when"] == nil)
+    let foreigner: [String: AnyHashable] = [
+      "timespans": [
+        [
+          // Starts and ends sometime today.
+          "start": [
+            "in": today,
+          ],
+          "end": [
+            "in": today,
+          ],
+        ],
+      ],
+      "duration": "PT1M", // 1 minute long
+      "label": "Today",
+    ]
+    json["when"] = foreigner
+    
+    let modifiedData = try JSONSerialization.data(withJSONObject: json, options: [])
+    let modifiedObject = try GeoJSON(data: modifiedData)
+    
+    let roundTrippedJSON = modifiedObject.toJSON()
+    
+    let when = try XCTUnwrap(roundTrippedJSON["when"] as? [String: Any?])
+    XCTAssertEqual(when as NSDictionary, json["when"] as? NSDictionary)
+  }
+  
+  func testForeignMemberCoding() throws {
+    let nullIsland = GeoJSON.Position(latitude: 0, longitude: 0)
+    try testForeignMemberCoding(in: .init(geometry: .single(.point(nullIsland))))
+    try testForeignMemberCoding(in: .init(geometry: .single(.lineString(.init(positions: [nullIsland, nullIsland])))))
+    try testForeignMemberCoding(in: .init(geometry: .single(.polygon(.init([[nullIsland, nullIsland]])))))
+    try testForeignMemberCoding(in: .init(feature: .init(geometry: .single(.point(nullIsland)))))
+    try testForeignMemberCoding(in: .init(features: []))
+  }
+  
+}