diff --git a/CalculatorReplicaSwiftUI/Helpers/OperationHandler/CalculatorOperationHandler.swift b/CalculatorReplicaSwiftUI/Helpers/OperationHandler/CalculatorOperationHandler.swift
index b3ff466..e8c36d3 100644
--- a/CalculatorReplicaSwiftUI/Helpers/OperationHandler/CalculatorOperationHandler.swift
+++ b/CalculatorReplicaSwiftUI/Helpers/OperationHandler/CalculatorOperationHandler.swift
@@ -16,7 +16,7 @@ final class CalculatorOperationHadler: CalculatorOperationHandlerProtocol {
 
     // MARK: - Stored properties
 
-    private var pendingBinaryOperation: PendingBinaryOperation?
+    private var pendingBinaryOperation: PendingBinaryOperationProtocol?
     private var isEnteringNumbers: Bool = false
     private var storedCalculatorDisplay: String = "" {
         didSet {
diff --git a/CalculatorReplicaSwiftUI/Scenes/Calculator/Operations/PendingBinaryOperation.swift b/CalculatorReplicaSwiftUI/Scenes/Calculator/Operations/PendingBinaryOperation.swift
index 2d31797..4624aec 100644
--- a/CalculatorReplicaSwiftUI/Scenes/Calculator/Operations/PendingBinaryOperation.swift
+++ b/CalculatorReplicaSwiftUI/Scenes/Calculator/Operations/PendingBinaryOperation.swift
@@ -6,7 +6,14 @@
 //  Copyright © 2020 Alonso. All rights reserved.
 //
 
-final class PendingBinaryOperation {
+protocol PendingBinaryOperationProtocol {
+    var hasOperand: Bool  { get }
+
+    func setOperand(_ secondOperand: Double)
+    func perform() -> Double
+}
+
+final class PendingBinaryOperation: PendingBinaryOperationProtocol {
     private let function: (Double, Double) -> Double
     private var accumulatedValue: Double
     private var operand: Double? = nil