C# MEF BrowserFactory for Browser Based Testing

In my browser based test framework I use MEF to help abstract the concept of a browser. The reason I do this is so I am not tied to a specific browser driver framework (e.g. WebDriver, WatiN, System.Net.WebClient). This allows me to change drivers without having to touch my test code. Here’s how I do it.

Browser Interface

First I created an interface that represents a browser. I used a mixture of interfaces from WebDriver and WatiN.

namespace CharlesBryant.TestPipe.Interfaces
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using CharlesBryant.TestPipe.Browser;
 using CharlesBryant.TestPipe.Enums;
public interface IBrowser
 IBrowserSearchContext BrowserSearchContext { get; }
BrowserTypeEnum BrowserType { get; }
string CurrentWindowHandle { get; }
string PageSource { get; }
string Title { get; }
string Url { get; }
ReadOnlyCollection WindowHandles { get; }
IElement ActiveElement();
void Close();
void DeleteAllCookies();
void DeleteCookieNamed(string name);
Dictionary<string, string> GetAllCookies();
bool HasUrl(string pageUrl);
void LoadBrowser(BrowserTypeEnum browser, BrowserConfiguration configuration = null);
void Open(string url, uint timeoutInSeconds = 0);
void Quit();
void Refresh();
void SendBrowserKeys(string keys);
void TakeScreenshot(string screenshotPath);
void AddCookie(string key, string value, string path = "/", string domain = null, DateTime? expiry = null);

Pretty basic stuff although BrowserSearchContext took some thought to get it working. Basically, this abstraction provides the facility to search for elements. A lot of the concepts here are borrowed from WebDriver and WaitN and are just a way to be able to wrap there functionality and use it without being directly dependent on them. To use this you have to change your tests from directly using a browser driver to using this abstraction. At the start of your tests you use the BrowserFactory to get the specific implementation of this interface that you want to test with.

Browser Factory

Then I created a BrowserFactory that uses MEF to load browsers that implement the browser interface. When I need to use a browser I call Create in the BrowserFactory to get the browser driver I want to test with. To make this happen I have to actually create wrappers around the browser drivers I want available. One caveat about MEF is that it needs to be able to find your extensions so you have to tell it where to find them. To make the browsers available to the factory I added an MEF class attribute, [Export(typeof(IBrowser))] to my browser implementations. Then I add a post build event to the browser implementation projects to copy their DLL to a central folder:

copy $(TargetPath) $(SolutionDir)\Plugins\Browsers\$(TargetFileName)

Then I added a appConfig key with a value that points to this directory to the config of my clients that use the BrowserFactory. Now I can reference this config value to tell MEF where to load browsers from. Below is sort of how I use the factory with MEF.

namespace CharlesBryant.TestPipe.Browser
 using System;
 using System.ComponentModel.Composition;
 using System.ComponentModel.Composition.Hosting;
 using System.Configuration;
 using System.IO;
 using System.Reflection;
 using CharlesBryant.TestPipe.Enums;
 using CharlesBryant.TestPipe.Interfaces; 

 public class BrowserFactory
 private IBrowser browser; 

 public static IBrowser Create(BrowserTypeEnum browserType)
 BrowserFactory factory = new BrowserFactory();
 return factory.Compose(browserType);

 private IBrowser Compose(BrowserTypeEnum browserType)
 this.browser = null; 

 AggregateCatalog aggregateCatalogue = new AggregateCatalog();
 aggregateCatalogue.Catalogs.Add(new DirectoryCatalog(ConfigurationManager.AppSettings["browser.plugins"])); 
 CompositionContainer container = new CompositionContainer(aggregateCatalogue);
 catch (FileNotFoundException)
 catch (CompositionException)

 return this.browser;

namespace CharlesBryant.TestPipe.Enums
public enum BrowserTypeEnum


Well that’s the gist of it. I have untethered my tests from browser driver frameworks. This is not fully tested across a broad range of scenarios so there may be issues, but so far its doing OK for me.

The examples above are not production code, use at your own risk.

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