Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Tests/A+/2.1.2.swift

@@ -0,0 +1,26 @@
+import PromiseKit
+import XCTest
+
+class Test212: XCTestCase {
+    func test() {
+        describe("2.1.2.1: When fulfilled, a promise: must not transition to any other state.") {
+            testFulfilled { promise, expectation, _ in
+                promise.test(onFulfilled: expectation.fulfill, onRejected: { XCTFail() })
+            }
+
+            specify("trying to fulfill then immediately reject") { d, expectation in
+                d.promise.test(onFulfilled: expectation.fulfill, onRejected: { XCTFail() })
+                d.fulfill()
+                d.reject(Error.dummy)
+            }
+
+            specify("trying to fulfill then reject, delayed") { d, expectation in
+                d.promise.test(onFulfilled: expectation.fulfill, onRejected: { XCTFail() })
+                after(ticks: 1) {
+                    d.fulfill()
+                    d.reject(Error.dummy)
+                }
+            }
+        }
+    }
+}