How to Implement Dependency Injection with POM in Playwright for Scalable Test Automation

#automation #pom #playwright

Modern test automation is no longer just about writing test scripts that click buttons and verify results. Today, scalability, maintainability, and reusability are crucial. As test suites grow, poorly structured code leads to duplicated effort, flaky tests, and high maintenance costs. This is where Playwright, Dependency Injection (DI), and Page Object Model (POM) come together to provide a clean, maintainable automation framework.

What is Playwright?

Playwright is a modern end-to-end testing framework developed by Microsoft. It supports multiple browsers (Chromium, Firefox, WebKit) and languages (C#, Java, Python, Node.js). Playwright enables you to automate web apps reliably with features such as auto-waiting, tracing, and cross-browser support.

Example:

Why Modern Test Automation Needs Better Design Patterns?

When projects grow, having hundreds of test scripts with repeated steps can make automation fragile and hard to maintain. Design patterns like POM and DI help organize code so that changes (like locator updates) only need to be done once.

Real-life Example: Imagine a login page where the username field’s locator changes. Without POM, you’d have to update the locator in 50+ test files. With POM, you update it in one place, and all tests use the updated locator automatically.

Dependency Injection (DI) in C# Automation

What is Dependency Injection in C#
Dependency Injection in C# is a design pattern used to reduce tight coupling between classes, making applications more flexible, maintainable, and easier to test. Traditionally, classes create their own dependencies using the new keyword, which makes the code rigid and hard to change. With DI, these dependencies are supplied from the outside through constructors, methods, or properties, so each class can focus only on its core functionality.

The .NET framework provides a built-in DI container that manages service registration (AddSingleton, AddScoped, AddTransient) and resolves them at runtime. This greatly improves unit testing because mock or fake services can be injected instead of real implementations. Overall, DI supports clean architecture by keeping components loosely coupled, improving scalability, and making future changes far easier.

Why DI Matters in Test Automation

Reduces Code Duplication
No need to create the same objects (drivers, page objects, utilities) again and again.
Improves Maintainability
A centralized place to manage all dependencies makes the framework easier to update.
Loose Coupling
Classes (like Page Objects or Services) don’t depend on concrete implementations.
You can replace or extend them easily.
Easy to Switch Environments/Drivers
Change browser (Chrome → Firefox) or environment (QA → Staging) without modifying test code.
Better Test Stability
DI can provide fresh instances of WebDriver or API clients per test, preventing test interference.
Supports Clean Architecture
Makes the framework more modular with separation of concerns.
Makes Unit Testing Easier
You can inject mock dependencies for utilities, reporting, or API services during test runs.
Centralized Object Creation
All object lifecycles are controlled from one place (e.g., startup or container).
Improves Reusability
Pages, helpers, and services can be reused easily because they don’t handle their own dependencies.
Scales Well for Large Frameworks
DI is almost essential when you have hundreds of tests and many components.

Types of DI

Constructor Injection: Most common, dependencies passed via the constructor.
Method Injection: Dependencies passed via method parameters.
**Property Injection: **Dependencies set via public properties.

Setting Up Playwright in a C# Project

Install Playwright in a C# Project
Run:

dotnet add package Microsoft.Playwright
dotnet build
playwright install Create and Run the First Test

Basic Playwright Commands

Launch Browser: await playwright.Chromium.LaunchAsync()
Navigate: await page.GotoAsync(“url”)
Actions: await page.FillAsync(selector, value), await page.ClickAsync(selector)
Assertions: Assert.Equal(expected, actual)
To know more, refer to the link below.

Understanding Page Object Model (POM) in Playwright

What is POM & Why It Matters
The Page Object Model (POM) is a simple but powerful design pattern that helps keep your test code clean and manageable. Instead of scattering selectors and UI interactions across test files, POM groups them into dedicated page classes. This makes your tests easier to read, reduces duplication, and keeps maintenance under control as your application grows. In Playwright, POM fits in naturally because of its clean structure and support for reusable components, making it easier to scale your automation suite without creating a mess behind the scenes.

Advantages