The COM (Component Object Model) Design Pattern for Automation with Selenium and Cucumber
The Component Object Model (COM) is a design pattern that allows you to structure tests in test automation projects. Inspired by the popular Page Object Model (POM), COM goes beyond handling entire pages and focuses on specific UI components, such as buttons, text fields, dropdown menus, or other reusable elements.
In this tutorial, we will explain how to implement COM to test a web application with Selenium WebDriver and Cucumber, and how this approach can make your tests more flexible, modular, and easier to maintain.
What is the COM (Component Object Model)?
The Component Object Model (COM) is an evolution of the POM model. Instead of modeling an entire page as an object with methods interacting with all the page elements, COM breaks the user interface into individual components, such as:
Buttons
Text fields
Dropdown menus
Search bars
Tables
Each component is encapsulated in a Java class, and its interactions are managed by specific methods, allowing each element to be maintained and tested independently. This improves code reusability, maintenance, and flexibility in tests.
Why Use COM Instead of POM?
Increased Modularity:
With COM, each component (like a button or text field) is an independent entity. If a component changes (for example, a button's text changes), you only need to modify the component class without affecting other components or pages. This allows for high modularity and prevents the need to modify entire pages for minor adjustments.
Reusability and Flexibility:
Components can be reused across multiple pages of the application, reducing code duplication. For example, a ButtonComponent can be used on any page where the button appears, reducing redundancy and increasing test flexibility.
Simplified Maintenance:
Maintenance is easier with COM. If a component changes (for example, a button or text field), you only need to modify the class representing that component. All tests using that component will be automatically updated without having to revisit each test scenario.
Adapted to Dynamic Interfaces:
Modern applications are often dynamic, with interfaces that change frequently. COM is ideal for such applications because it allows testing of components independent of the interface. You can modify or add components without affecting tests for other parts of the application.
Faster Test Automation:
COM speeds up test automation. By centralizing interactions with components into reusable classes, testers don’t need to redefine actions for every page or component. For instance, a single step definition for the action "click a button" can be used across all tests in the project, significantly reducing the time needed to automate tests.
Avoiding Repetition of Work Between Testers:
With COM, testers no longer need to repeat the same work for every test. Centralized step definitions for common actions, such as "click a button" or "enter text," can be used by all testers in the project. This ensures consistency in tests while avoiding unnecessary repetition, improving efficiency and collaboration among testers.
COM Project Architecture
The architecture of a COM-based project is structured around three main elements: components, step definitions, and the runner.
Components:
Each component represents a UI element, such as a button, text field, or dropdown menu. These classes encapsulate all possible interactions with the element.
Here’s an example of the ButtonComponent
class:
public class ButtonComponent {
private WebDriver driver;
public ButtonComponent(WebDriver driver) {
this.driver = driver;
}
public void clickButton(String buttonText) {
WebElement button = driver.findElement(By.xpath("//button[text()='" + buttonText + "']"));
button.click();
}
}
Step Definitions:
Step definitions link the steps defined in the Gherkin files to the methods in the components. They are responsible for interacting with the components and implementing the actions specified in the test scenario.
Here’s an example of ButtonStepDefinition
:
public class ButtonStepDefinition {
private ButtonComponent buttonComponent;
public ButtonStepDefinition(WebDriver driver) {
this.buttonComponent = new ButtonComponent(driver);
}
@When("I click on the button {string}")
public void iClickOnTheButton(String buttonText) {
buttonComponent.clickButton(buttonText);
}
}
Runner:
The runner class is responsible for running the tests using JUnit or TestNG. It configures Cucumber to load the test scenarios defined in the .feature
files and run them using the step definitions.
Here’s an example of TestRunner
:
@RunWith(Cucumber.class)
@CucumberOptions(
features = "src/test/resources/features",
glue = "com.componentObjectModel.stepDefinitions",
plugin = {"pretty", "html:target/cucumber-reports.html"}
)
public class TestRunner {
}
Writing and Explaining a Gherkin Scenario
One of the essential elements of automation with Cucumber is using the Gherkin language to write test scenarios. Gherkin allows you to describe tests in a readable and understandable way, even for non-technical people.
Let’s consider a scenario where we want to test the interaction with a button, using the ButtonComponent
we defined earlier. Here’s how it might be written in Gherkin:
Scenario: User clicks on the "Submit" button
Given I am on the login page
When I click on the button "Submit"
Then I should be redirected to the homepage
Explanation of the scenario:
Scenario: This scenario describes the action where a user clicks the 'Submit' button on the login page and ensures they are redirected to the homepage after clicking.
Given I am on the login page: The initial state of the test is that the user is on the login page.
When I click on the button “Submit”: The action performed in the test is clicking the 'Submit' button.
Then I should be redirected to the homepage: The expected verification is that the user is redirected to the homepage after clicking the button.
Link with COM:
Each step in this scenario is mapped to a step definition in ButtonStepDefinition, where the click action is handled by the ButtonComponent, making the test modular and easy to maintain.
Additional explanation:
Notice that the steps take the displayed text on the buttons (or placeholders in input fields, etc.) as parameters. This makes the scenarios more readable and generic. For example, in the scenario above, the text of the button "Submit" is used directly in the step "When I click on the button 'Submit'". In this way, the same step definition could be reused to test another button, such as "Login", by simply changing the text in the Gherkin scenario. This improves the reusability of the test code, while making the scenarios more intuitive and flexible
Reusability of Steps with COM
One of the key advantages of COM is the reusability of step definitions for different buttons. For example, the same step `When I click on the button {string} can be used for all buttons, regardless of the text displayed on the button. The COM approach allows you to dynamically parameterize the click action based on the button text.
Let’s consider another scenario with a different button:
Scenario: User clicks on the "Login" button
Given I am on the login page
When I click on the button "Login"
Then I should be redirected to the dashboard
In both cases, the same clickButton method in the ButtonComponent will be used, but the button text will change depending on the scenario. This demonstrates how COM allows reusing the same component and step definition, making tests flexible and modular.
How COM Improves Test Automation
COM improves test automation in several ways:
Reduction of Code Duplication: By using reusable components, you reduce code duplication in tests. For example, a ButtonComponent
used in multiple pages of the application eliminates the need to write repetitive tests.
More Readable and Modifiable Tests: Tests are clearer and easier to understand, as they are decoupled from page-specific implementation details. You can focus on interacting with components, without worrying about the underlying page structure.
Ease of Maintenance: Any modification to a component (e.g., a button text change) only affects the component class, not the tests. This makes maintenance much simpler and faster.
More Flexible Tests: Tests can easily be adapted to changing UIs, as components are independent of each other. You can test new components or replace existing ones without affecting other tests.
When is the COM (Component Object Model) Design Pattern Recommended?
This design pattern is recommended if the web application being tested uses a unified design system for all components. For example, if all buttons are declared in the same way, with a consistent structure for all UI elements. In such cases, using COM allows you to centralize interactions with each type of component (such as buttons, text fields, etc.), making tests more modular, reusable, and easier to maintain.
Reusing Step Definitions Across Multiple Products
If you are developing and testing multiple products that use the same design system, you can create a library that encompasses all the step definitions and actions (or almost all) for each component. This allows testers to focus solely on writing Gherkin scenarios, and the tests will be automated. Since all web elements are written in the same way (HTML), components like buttons, text fields, and other UI elements will behave consistently across all projects.
As a result, testers no longer need to repeat the same tasks—defining step definitions and actions for identical components across multiple projects. This approach saves time and improves maintainability. If a web element is modified (for example, if the XPath changes), you only need to update that element in the shared library, and the modification will be automatically applied to all automation projects. This reduces the risk of errors and makes updates more efficient across different products.
Conclusion
The Component Object Model (COM) is a powerful design pattern for organizing test automation. By focusing on reusable components, COM allows you to create more modular, maintainable, and scalable tests. This pattern is particularly useful for modern applications, where the user interface changes quickly, and where interacting with independent components is essential.
With reusable tests, simplified maintenance, and a flexible architecture, COM is the ideal solution for test automation in Selenium and Cucumber projects.
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