add test for parsing double encoded utf8

SocketIO-MacTests/SocketEngineTest.swift

@@ -74,4 +74,18 @@ class SocketEngineTest: XCTestCase {
         engine.parseEngineMessage("afafafda", fromPolling: false)
         waitForExpectationsWithTimeout(3, handler: nil)
     }
+    
+    func testEngineDecodesUTF8Properly() {
+        let expectation = expectationWithDescription("Engine Decodes utf8")
+        
+        client.on("stringTest") {data, ack in
+            if let str = data[0] as? String {
+                assert(str == "lïne one\nlīne \rtwo", "Failed string test")
+                expectation.fulfill()
+            }
+        }
+
+        engine.parsePollingMessage("41:42[\"stringTest\",\"lïne one\\nlīne \\rtwo\"]")
+        waitForExpectationsWithTimeout(3, handler: nil)
+    }
 }