Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Tests/A+/2.3.1.swift

@@ -0,0 +1,31 @@
+import PromiseKit
+import XCTest
+
+class Test231: XCTestCase {
+    func test() {
+        describe("2.3.1: If `promise` and `x` refer to the same object, reject `promise` with a `TypeError' as the reason.") {
+            specify("via return from a fulfilled promise") { d, expectation in
+                var promise: Promise<Void>!
+                promise = Promise().then { () -> Promise<Void> in
+                    return promise
+                }
+                promise.catch { err in
+                    if case PMKError.returnedSelf = err {
+                        expectation.fulfill()
+                    }
+                }
+            }
+            specify("via return from a rejected promise") { d, expectation in
+                var promise: Promise<Void>!
+                promise = Promise<Void>(error: Error.dummy).recover { _ -> Promise<Void> in
+                    return promise
+                }
+                promise.catch { err in
+                    if case PMKError.returnedSelf = err {
+                        expectation.fulfill()
+                    }
+                }
+            }
+        }
+    }
+}