import UIKit
import RxSwift
import SlackWebAPIKit

class ViewController: UIViewController {

    let postUserMessageUseCase = FindUserAndPostMessageUseCase()
    let disposeBag = DisposeBag()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        postUserMessageUseCase.execute(text: "Test", user: "alberto")
            .subscribe(onNext: { (isSent) in
                print("onNext \(isSent)")
            }, onError: { (error) in
                print("onError \(error)")
            }, onCompleted: {
                print("onComplete")
        }).addDisposableTo(disposeBag)
    }
}


import UIKit
import SlackWebAPIKit

class ViewController: UIViewController {

    let postUserMessageUseCase = FindUserAndPostMessageUseCase()
    
    override func viewDidLoad() {
        super.viewDidLoad()
     
        _ = postUserMessageUseCase.execute(text: "Test", user: "alberto")
            .subscribe(onNext: { (isSent) in
                print("onNext \(isSent)")
            }, onError: { (error) in
                print("onError \(error)")
            }, onCompleted: {
                print("onComplete")
            })
    }
}


--- 
+++ 
@@ -1,21 +1,23 @@
 import UIKit
+import RxSwift
 import SlackWebAPIKit
 
 class ViewController: UIViewController {
 
     let postUserMessageUseCase = FindUserAndPostMessageUseCase()
+    let disposeBag = DisposeBag()
     
     override func viewDidLoad() {
         super.viewDidLoad()
-     
-        _ = postUserMessageUseCase.execute(text: "Test", user: "alberto")
+        
+        postUserMessageUseCase.execute(text: "Test", user: "alberto")
             .subscribe(onNext: { (isSent) in
                 print("onNext \(isSent)")
             }, onError: { (error) in
                 print("onError \(error)")
             }, onCompleted: {
                 print("onComplete")
-            })
+        }).addDisposableTo(disposeBag)
     }
 }
 
Create dispose bag property in example
