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Wednesday, 8 June 2011

Why WatiN tests are slow with the IE browser

I found opening and closing of the IE browser in WatiN a massive overhead when I was having to dispose of IE at the end of each of NUnit's tests. I found a way though to speed the whole process up.

I really wanted to open one instance of IE in my NUnit TestFixture and use that for the duration. This would save the huge huge cost of opening and disposing of WatiN's IE browser. As a sidenote it was a lot quicker in FireFox but since most users use IE best stick to that!

There were a couple of hurdles to jump to enable me to use just one IE browser for all my NUnit TestFixture's WatiN tests though.

1. Initialise and Dispose of IE at either end of the TestFixture

This is fairly obvious if you are familiar with NUnit. You just need to utilise the TestFixtureSetUp and TestFixtureTearDown attributes to initialise and dispose of your IE browser like so:
public class MyTests : IDisposable
    IE Browser;
    public void Init()
        Browser = new IE();

    public void Dispose()
        if (Browser != null)


TestFixtureTearDown will run regardless of any fails in Assertions or even Exceptions so you can be confident that the browser will close on any unmaned CI machines.

2. Solving the weird STA problem (in NUnit)

You need to add to your app.config to ensure the tests run in an single thread apartment (STA) so that the non thread safe Internet Explorer browser can run safely.

I have written separately about how to solve the STA threading problem in Internet Explorer for WatiN.

The overhead of opening and closing the Internet Explorer browser should now be reduced to a one off. I have seen tests times of my NUnit powered WatiN tests reduce from 12 mins down to just 51 secs!

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  1. With nUnit you also have the SetupFixture if you have more than one class.

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