Stubbing not working with Alamofire manager

Tests.swift

func testExample() {
        let expectation = expectationWithDescription("test expectation")
        let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
        configuration.timeoutIntervalForRequest = 30

        let alamofireManager = Manager(configuration: configuration)
        let body = ["json": "test"]
        stub(everything, builder: json(body))

        alamofireManager.request(.GET, "https://www.test.com").responseJSON { response in
            switch response.result {
            case .Success(let JSON):
                print(JSON)
                expectation.fulfill()
            case .Failure(let error):
                print(error)
            }
        }
        waitForExpectationsWithTimeout(5.0, handler: nil)
    }