The old adage of testing UIs

UI testing, especially if it is automated, has been a bullseye hard to hit when comes to software development. It is a cornerstone of delivering reliable and user-friendly desktop applications. It’s an essential practice for ensuring the quality and functionality of the user interface (UI), which is often the most visible and interacted-with component of an application. In this article, we delve into three popular approaches to automated UI testing for desktop applications: Sikuli, Selenium, and Model-View-ViewModel (MVVM) based solutions.

Sikuli: Visual Automation Testing

Sikuli represents a unique approach to UI testing by leveraging image recognition technology. It allows testers to automate desktop applications by visually searching for UI elements, rather than relying on internal UI structure or code. This method is highly effective in situations where traditional object-based identification is challenging.

Key Features:

  • Visual Match: Sikuli operates by matching screenshots of UI elements, making it intuitive and less reliant on underlying UI framework details.
  • Scripting Flexibility: It uses a simple scripting language that integrates with Python, enabling the creation of complex test scenarios.
  • Cross-Platform Compatibility: Sikuli can be used for testing desktop applications across various operating systems.

Pros and Cons:

  • Advantages: Ideal for applications with dynamic UIs and for scenarios where internal UI structures are inaccessible or unreliable.
  • Limitations: The accuracy can be affected by screen resolution and color scheme changes.

Sikuli excels in situations where you need to identify and interact with UI elements based on their visual appearance.

Scenario: Testing a calculator application where you need to click the buttons ‘5’, ‘+’, ‘2’, and ‘=’ to perform an addition.

# Sikuli script to test a simple addition in a calculator app
from sikuli import *

# Path to images of calculator buttons
five_button = "five_button.png"
plus_button = "plus_button.png"
two_button = "two_button.png"
equals_button = "equals_button.png"

# Click the '5' button

# Click the '+' button

# Click the '2' button

# Click the '=' button

# Verify the result (assuming the result is visible in a specific region)
result_region = Region(10,10,100,20)
if result_region.exists("7.png"):
    print("Test Passed")
    print("Test Failed")

Selenium: A Versatile Web and Desktop Testing Tool

Originally designed for web applications, Selenium also extends its capabilities to desktop applications, particularly those with web-based UIs or embedded web components.

Key Features:

  • WebDriver: Selenium WebDriver interacts with the UI elements of the application, simulating real-user interactions.
  • Language Support: Supports multiple programming languages like Java, C#, Python, allowing integration into diverse development environments.
  • Community and Ecosystem: Has a large community, extensive documentation, and numerous third-party tools for enhanced testing capabilities.

Pros and Cons:

  • Advantages: Highly effective for applications with web-based UI components; supports a wide range of browsers and platforms.
  • Limitations: More suited for web components; can be complex to set up for pure desktop application UIs.

Selenium is ideal for automating web-based components within desktop applications or applications that expose their UI elements in a web-like structure.

Scenario: Automating a form submission in a desktop application with embedded web components.

# Selenium script to fill out and submit a form
from selenium import webdriver
from import By

# Setting up WebDriver (assuming appropriate driver for the desktop application)
driver = webdriver.Chrome()

# Navigate to the form

# Fill out the form fields
driver.find_element(By.ID, "name_input").send_keys("John Doe")
driver.find_element(By.ID, "age_input").send_keys("30")

# Click the submit button
driver.find_element(By.ID, "submit_button").click()

# Verify submission (checking for a confirmation message)
confirmation = driver.find_element(By.ID, "confirmation_message").text
assert "Thank you" in confirmation


MVVM-Based Solutions: Leveraging Architectural Patterns

Model-View-ViewModel (MVVM) is a software architectural pattern primarily used in developing user interfaces. In the context of automated UI testing, it separates the development of the graphical user interface from the development of the business logic or back-end logic of the application. This separation allows for more manageable, scalable, and testable code.

Key Features:

  • Separation of Concerns: By decoupling UI from business logic, it enables more focused and efficient testing.
  • Data Binding: MVVM facilitates automated testing by using data binding, allowing tests to interact with the UI logic rather than UI elements directly.
  • Test Frameworks Integration: Easily integrates with test frameworks like NUnit, xUnit, enabling comprehensive unit and UI testing.

Pros and Cons:

  • Advantages: Facilitates maintainable and scalable code; ideal for large and complex applications with extensive UI logic.
  • Limitations: Requires initial learning curve and strict adherence to the MVVM pattern; may not be necessary for simpler applications.

In MVVM architecture, UI testing often focuses on the ViewModel, which acts as an intermediary between the View and the Model, enabling easier testing of UI logic.

Scenario: Testing a ViewModel in a WPF (Windows Presentation Foundation) application.

// C# NUnit test for a ViewModel in an MVVM architecture
public void TestAdditionCommand()
    // Arrange: Create ViewModel with necessary dependencies
    var calculatorViewModel = new CalculatorViewModel();

    // Set the inputs
    calculatorViewModel.Input1 = "5";
    calculatorViewModel.Input2 = "2";

    // Act: Invoke the command that triggers addition

    // Assert: Verify the outcome is as expected
    Assert.AreEqual("7", calculatorViewModel.Result);


Automated UI testing for desktop applications is an evolving field with multiple approaches, each suited to different types of applications and development methodologies. Sikuli offers a unique visual approach, Selenium extends its robust web testing capabilities to desktops, and MVVM-based solutions provide a structured way to manage and test complex UIs. The choice between these solutions depends on the specific needs and context of the project, including the nature of the application’s UI, the development team’s expertise, and the overall project requirements. With the right tools and strategies, automated UI testing can significantly improve the quality and reliability of desktop applications.

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