Guarantees support for async<T>

Sources/AwaitKit/AwaitKit.swift

@@ -43,6 +43,15 @@ public func async<T>(_ body: @escaping () throws -> T) -> Promise<T> {
   return Queue.async.async(.promise, execute: body)
 }
 
+/**
+ Yields the execution to the given closure and returns a new guarantee
+ - parameter body: The closure that is executed on a concurrent queue.
+ - returns: A new guarantee that is resolved when the provided closure returned.
+ */
+public func async<T>(_ body: @escaping () -> T) -> Guarantee<T> {
+    return Queue.async.async(.promise, execute: body)
+}
+
 /**
  Yields the execution to the given closure which returns nothing.
  - parameter body: The closure that is executed on a concurrent queue.

Tests/AwaitKitTests/AwaitKitAsyncTests.swift

@@ -53,6 +53,26 @@ class AwaitKitAsyncTests: XCTestCase {
     }
   }
 
+    func testSimpleDelayedValidGuaranteeAsyncBlock() {
+        let expect = expectation(description: "Async should return value")
+
+        let guarantee: Guarantee<String> = async {
+            Thread.sleep(forTimeInterval: 0.2)
+
+            return "AwaitedPromiseKit"
+        }
+
+        _ = guarantee.done { value in
+            expect.fulfill()
+        }
+
+        waitForExpectations(timeout: 0.5) { error in
+            if error == nil {
+                XCTAssertEqual(guarantee.value, "AwaitedPromiseKit")
+            }
+        }
+    }
+
   func testSimpleFailedAsyncBlock() {
     let expect = expectation(description: "Async should not return value")